How many oxygen sensors are on a 1997 Chevrolet s10 and where they located?

A 1997 Chevrolet S10 typically has one oxygen sensor. It's located in the exhaust system, before the catalytic converter. The exact location will vary slightly depending on the engine configuration (4.3L V6 or 2.2L I4), but it's generally near the engine's exhaust manifold or very close to where the exhaust manifold joins the rest of the exhaust system.