My EmailSMTP uses the Windows API functions mentioned in other answers to generate a UUID.

http://www.topwizprogramming.com/freecode_emailsmtp.html

Here another way with external functions:

// external functions

Function long UuidCreate ( Ref os_UUID pId ) Library "rpcrt4.dll"

Function long UuidToString ( Ref os_UUID Uuid, Ref ulong StringUuid ) Library "rpcrt4.dll" Alias For "UuidToStringW"

Function long RpcStringFree ( Ref ulong pString ) Library "rpcrt4.dll" Alias For "RpcStringFreeW"

Subroutine CopyMemory ( Ref string Destination, ulong Source, long Length ) Library  "kernel32.dll" Alias For "RtlMoveMemory"

// structure

type os_uuid from structure
    unsignedlong        data1
    integer        data2
    integer        data3
    blob        data4
end type

//Function of_generate_guid

os_UUID lstr_UUID
Constant Long RPC_S_OK = 0
Constant Long SZ_UUID_LEN = 36
ULong lul_ptrUuid
String ls_Uuid

lstr_UUID.Data4 = Blob(Space(8), EncodingAnsi!)
If UuidCreate(lstr_UUID) = RPC_S_OK Then
    If UuidToString(lstr_UUID, lul_ptrUuid) = RPC_S_OK Then
        ls_Uuid = Space(SZ_UUID_LEN)
        CopyMemory(ls_Uuid, lul_ptrUuid, SZ_UUID_LEN * 2)
        RpcStringFree(lul_ptrUuid)
        ls_Uuid = Upper(ls_Uuid)
    End If
End If

Return ls_Uuid

1.  Create a global external function

FUNCTION long uuidCreate(ref s_uuid astr_uuid) LIBRARY "Rpcrt4.dll"  ALIAS FOR "UuidCreate"

*********************************************************************************************************************

2.  Create a global function f_generate_uuid

Function f_generate_uuid(String as_type)

It seems that there are a number of way to generate GUID in DB2, have you looked at the link below:

https://www.ibm.com/developerworks/community/blogs/SQLTips4DB2LUW/entry/generating_universally_unique_identifiers_uuid63?lang=en

You should be able to utilise any of these methods within PB.

Regards

David