The baggage allowance will be the allowance for the marketing carrier of the first segment. UA is the marketing carrier, thus the UA baggage allowance for SOF-VIE. In theory this only applies to the base allowance, but as both OS and UA are *A, OP will get the extra bag from both.

This information should be on OP's e-ticket. The time to get any discrepancies taken care of is now, not the airport, because the check-in agent will see the same information on his screen as OP sees on his e-ticket receipt.