As long as both files are set to the proper record, in Panorama 6 you could simply use:
Window "TEST:TRIP"
ID01=grabdata("Membership File",«ID Number»)
while in Panorama X the grabdata( function has been changed to fieldvalue(:
Window "TEST:TRIP"
ID01=fieldvalue("Membership File",«ID Number»)
or alternately:
setactivedatabase "TEST"
ID01=fieldvalue("Membership File",«ID Number»)
setactivedatabase ""