how do I know whether I am currently in chained or unchained mode
Sybase ASE's default mode is unchained, as I suspect you already know.

You can use SELECT @@tranchained; to see the status for the current session's transaction chaining mode.

The result is either 0 or 1, per the following:

0 = unchained
1 = chained


Transaction chaining mode can be modified with SET CHAINED ON; or SET CHAINED OFF;