Are you looking for the spid or the command that generated the 701?
Where are you seeing the 701 error?
If the error's showing up in an application log (eg, 'isql' output) then shouldn't this give you an idea as to the command that generated the 701?
If you really want the spid you could try querying master..monSysStatement, looking for ErrorStatus = 700 ... though I've found this isn't 100% reliable.