To pinpoint the exact location, you'll need to:
1. Consult your vehicle's repair manual: This is the best resource as it will have diagrams showing the exact location of the oxygen sensors for your specific engine.
2. Use a repair database (online): Websites like AllDataDIY, Mitchell 1, or Chilton offer diagrams and repair information for a fee, but often provide more detailed information than a generic manual.
3. Look for them visually: Once you have a general idea from your manual or database, you can visually inspect the exhaust manifold and pipe near the engine. They're usually threaded into the exhaust system and have a wire harness connected to them. Be careful; the exhaust system will be hot even after the engine has been off for a while.
Without knowing your specific engine size, I cannot give you a precise location. Always refer to a repair manual or database for your specific vehicle to avoid potential damage or incorrect replacement.