what is , and where is axillary shaft?

that is the short shaft that runs from the engine looks like a small drive shaft That is for the water pump and belts under hood Because your engine is in middle just replace it

Don't replace the shaft- replace the bushings on the shaft. It's a difference between $1,000 plus for a new shaft and under $500 to have a shop replace the bushings. The bushings go bad on high mileage Previas.