$661
The call itself will be either FM SWF_EVT_HANDLER_START_INTERNAL or more likely SWW_WI_EXECUTE_INTE
The call itself will be either FM SWF_EVT_HANDLER_START_INTERNAL or more likely SWW_WI_EXECUTE_INTERNAL_RFC (depending on scenario). That is the one you want to either externally debug OR set a break-point for yourself in the calling program and then switch to system debugger as described before.
Side note: as this sort of this is not an everyday occurrence and switching the RFC user in the Workflow connection to SERVICE temporarily is dangerous (depending on it's authorizations...), would it not be easier to have an emergency access procedure to temporarily grant yourself some more powers and debug it from SM66.
What I am describing above has actually been more a workaround to debug the workflow anyway as the RFC user and not really the best solution tailored onto to authorizations that you need temporarily.
However if the RFC user has ACTVT 02 and 70 then you are home and dry to go to SM66 as the RFC user instead... in that case you can set your break-point where ever you want to as all you want is a session back from the destination.
Just my opinion.
Cheers,
Julius