Is there a manual release for the rear window hatch on 1995 S10 Blazer?

No, the 1995 S10 Blazer does not have a manual release for the rear window hatch. The hatch is only operable via the power switch on the dash or the key fob (if equipped). If the power system fails, the hatch will be stuck. You'll need to troubleshoot the electrical system or find other ways to open it (potentially requiring some disassembly).