there should be a label on the radiator support or under the hood saying what you have.
If I remember right it was around '93 or '94 that they switched from R12 to r134a. My '93 S10 had r12 but my brother’s '95 S10 had r134a.
And no you cant put r12 in an r134a system and youd need to convert an r12 system to run r134a