I have an outdoor covered deck which has six recessed can lights which are currently controlled by on/off switches located at the family room entrance to the deck and at the master bedroom entrance to to the deck. Can I put a dimmer switch on either or both of these switch locations and will it work.

Yes, just buy a 3 way dimmer switch with a wattage rating higher then the total wattage of your 6 bulbs. Remove the 3 way switch that has the main power going to it and install the dimmer switch. You should have a wiring diagram with the dimmer. Do not do anything to the other 3 way switch.