The smell of burning clutch. Loss of power coupled with clutch slippage when clutch is out. You will experience difficulty moving from a stop, driving up hills, etc. The engine will rev higher than normal to get at speed.
A way to test is to drive to a big empty parking lot and park the car. From a stop with the clutch in, your foot on the brakeand the engine running, slowly let the clutch out. If you can let the clutch out a couple of inches without bogging the engine, then the clutch is slipping