You can set the breakpoint with the command
Break.Set /Program /CMD "DO myScript.cmm"
To continue the execution of the target program, add the command Go to the end of the called PRACTICE script.
The Break.Set command also accepts the option /RESUME which will resume the program execution after the command DO myScript.cmm is executed. This is however not suitable in this case, since it won't wait until the called PRACTICE script has finished.