My wife has no income. How much could I contribute to her RRSP if I used out my own RRSP room

If you used up your own RRSP contribution room, you will not be able to contribute to a spousal RRSP.  The amount you can contribute is based on your own contribution room.

For more information on Spousal RRSPs:

https://turbotax.intuit.ca/tips/spousal-rrsps-in-canada-6353