Where is the other end of negative battery cable connected to in 1988 Corvette?

Negative Battery Cable Termination Points

Since I have no experience with Corvettes, this answer will of necessity be generic in nature until a Corvette expert can improve it.

General Motors vehicles usually connect the "other" end of the Negative Battery Cable somewhere on the engine block.

Usually this is done under one of the heavy bolts used to secure the exhaust manifold on the battery side of the engine, or under one of the bolts attaching an auxiliary bracket [as for the pollution control air compressor, or an alternator bracket.