how to find out the reason for blocking locks?

PB Application try to create data in ASE 12.5. With this operation, there are sql, sp, trigger involved. Most of the it is okay. With lock of sleeping or sync sleeping lock. User wait for a short time to get the result.

but some time, there are blocking lock.

If spid for the app is 1. then looks like this app also generate another spid, say it is 2. and 2 is blocking by 1. spid 1 holding lock!

then all user is frozen because of spid 1 holding lock!!! How to figure it out the reason for blocking locks?