In general, $extract() and $zstrip() are your friends.
If you want to strip ONLY the LAST character, then use this

set data="abc,,"
set $extract(data,*)=""
write data --> abc,

If you want to strip ALL (same) trailing characters, use this

set remove=","
set data1="abc,"
set data2="abc,,,"
set data3="abc,,-,,"
set data1=$zstrip(data1,">",remove)
set data2=$zstrip(data2,">",remove)
set data3=$zstrip(data3,">",remove)

write data1 --> abc
write data2 --> abc
write data3 --> abc,,-

If you know which record is locked (i.e. ^My.Global(123) ) then you can identify the locking process (and therefore the user) in a simple method

Class DC.Lock Extends %RegisteredObject
{
/// For a given (global) reference
/// return the (exclusive) locking processID and username
/// 
/// ref: a global reference, for example: $name(^My.Global(1,2,3))
/// 
/// For other lock types (shared, remote)
/// use the infos obtained by info_types OWNER, MODE, FLAGS and COUNTS, see
/// https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_slock
/// 
ClassMethod Who(ref)
{
    if ^$LOCK(ref,"MODE")="X" {
        set pid=^$LOCK(ref,"OWNER")
        if pid {
            set job=##class(%SYS.ProcessQuery).%OpenId(pid)
            quit {"pid":(pid), "usr":($s(job:job.UserName,1:""))}
        }
        
    } else  { quit {} }
}
}

For example:

set ref=$name(^My.Global(123))
lock +@ref:1
if '$test {
    // in case, the node is locked,
    // check up, by who is the node locked
    set who=##class(DC.Lock).Who(ref)
    write who.%ToJSON() --> {"pid":"2396","usr":"kav"}
}

Take a look on %SYSTEM.OBJ class

do $system.OBJ.Compile("your.classname")
// or to compile a whole package
do $system.OBJ.CompilePackage("your.package")

 /// Use the propertydefinition-class:
 /// Open your.classname || propertyname
 /// For example:
 set def=##class(%Dictionary.PropertyDefinition).%OpenId("Sample.Person||Name")
 if def write def.Type
 
 

the above approach ist the right way. And I do not see any problem there:

First, in the very first line (of the question) it's stated: "I need to develop a tool ... what data is being consumed by a certain process, ... to build an automated test scenario.", which means, this will be used during a development and/or test phase to gather informations about the touched globals (for automated tests). So the performance is not an issue.
 
Second, the suggestion of Paul Waterman can always run, assuming the process runs with the required right and flag. One can always provide the required conditions.

Some twenty years ago,  SOAP was a hype and catchword like today ML, AI and Python are and everybody (includen me) used SOAP.
At those times I used tcpTrace (https://www.pocketsoap.com/tcptrace/) for debugging. I can't you help more than that.

Your example shows https but you try a http connection.   Is this a mistake or a typo?

Usually, you get a <COMMAND> error, if you call a (class)method as an expression but the called method does not provide a value 

Method SomethingErr()
{
    write "Hello"
}

Method SomethingOk()
{
    quit "Hello"
}


do ..SomethingErr() // this is OK
do ..SomethingOK()  // this is OK
write ..SomethingErr() // gives a <COMMAND> error
write ..SomethingOK()  // is OK

As an addition to the above said

set mydir="C:\dir1\dir2\newdir"
//
// creates newdir ONLY if dir1 and dir2 exists
write ##class(%File).CreateDirectory(mydir)

// creates newdir and, IF NECESSARY, the intermediate directories dir2 and dir1 too
write ##class(%File).CreateDirectoryChain(mydir)

Some remarks:

 // on Linux, it's a good idea to limit the ping count
 set cmnd="ping -c 3 "_host
 
 // if $zeof isn't alway on, as on my systems the case is
 // we need two more lines
 set cmd="..."
 set old=$system.Process.SetZEOF(1)  // turn $ZEOF on
 open cmd...
 ...
 close cmd
 do $system.Process.SetZEOF(old)     // reset to old state

Four short lines of Objectscript code

ClassMethod Ping(host)
{
	set cmd="ping "_host
	open cmd:"QR":10
	for {use cmd read ans quit:$zeof  use 0 write ans,!}
	close cmd
}

// some test
do ##class(your.class).Ping("google.com")

Pinging google.com [142.250.185.110] with 32 bytes of data:
Reply from 142.250.185.110: bytes=32 time=25ms TTL=114
Reply from 142.250.185.110: bytes=32 time=26ms TTL=114
Reply from 142.250.185.110: bytes=32 time=19ms TTL=114
Reply from 142.250.185.110: bytes=32 time=19ms TTL=114

Ping statistics for 142.250.185.110:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 19ms, Maximum = 26ms, Average = 22ms

also, you could try the 

$SCONVERT(s,format,endian,position)

function (Format: F4)

set name = $name(^A)
for i=1:1:10 { set name = $name(@name@("TEST"_i)) }
set @name=""

Two more bytes and the problem is solved:

Property refDate As %Date [InitialExpression = {$piece($horolog,",",1)}];
//.............................................^......................^

Caution,  backward $order() is always slower than forward $order(). If you need the last (hopefully few) entries, than it's OK to use a backward-$O() but running (counting) from the bottom to the top over several millions of nodes is definitely not an effective run.

As others already wrote,

write $order(^$GLOBAL(""))

gives you the first global name accessible from a given namespace. Usually, this will be a percent-global (^%...) but if you want to get the first (or all) global, which resides in a given database, the do the same as above but with extended global access

set dir = "^^c:\databases\mydb\"  // "^^" and "the path to your CACHE/IRIS.dat file"
write $order(^$|dir|GLOBAL(""))

There are several possibilities, using WinSCP  from Windows, Linux and Samba, etc. But if "using Cache codes" (Objectscript) is a  requirement, then the simplest way is: open a TCP-(server)port on the one end and a TCP-(client)port on the other end, write and read the data, close the connections. Voila. The job is done. I do not see any problem there. OK, maybe you need to open those ports. And do not forget, USB-Sticks exists too ;-))

I'm not aware of any $ISJSON() or similar named function but you can easily make your own

ClassMethod IsJSON(str)
{
	try { ret:{}.%FromJSON(str) 1 } catch e { ret:e.Code=3 0 throw e }
}

set a="{name:""John Doe"" "
set b="{""name"":""John Doe"" }"

write ##class(some.class).IsJSON(a) --> 0
write ##class(some.class).IsJSON(b) --> 1
write ##class(some.class).IsJSON()  --> <UNDEFINED>zIsJSON+1^...  *str

As an addition to the above possibilities, you can  ALWAYS use (assumed, you have the rights to access the database where the global lives - this is true for both of the above too) extended global access.

Just one remark, this kind of access is possible but not the recommended way for creating regular classes (databases) rather to occasionally (on demand) access data from other namespace and/or namespaces.

set nsp = "USER"
set myvar = ^|nsp|MyGlobal(1,2,3)

If there is no namespace associated with the database (where the global lives) just use the implicit namespace

set dir = "^^C:\mydatabases\myfolder\"    // win-world, "^^pathToTheDatabase"
set dir = "^^/opt/mydatabases/myfolder/"  // unix-world, 
write ^|dir|myglobal(1,2,3)

// and, of course all other commands and functions
kill ^|dir|myglobal(1)
write $order(^|dir|myglobal(1,2))
set isDef = $data(^|dir|myglobal)