I would like to know what should my pressures read on the low/high side of my outside condenser using R-22 and its a 2 ton unit and the ambient temp is 75 degrees (F)? Thanks

The pressure will vary as the temperature varies in the house as well as outside of the house.
To be accurate with the presures you have to have set of gauges and some electronic thermostats to measure the tempature of the freon inside the pipes.

But if you are just trying to get a close charge on your unit there are a couple of rule of thumbs tests. One of which it the cold beer can method. With the unit running put you hand on the suction pipe of the system and start adding gas, when the suction line becomes as cool as a can of beer you would drink you will have it close.
Another is to measure the temp of the air being pulled into the return air just under the furnace or air handler, now measure the temp just above the evap coil, there should be an 18 to 20 degree difference in the temps.

Neither way is 100% and can be off by quite a bit because of differences in humidity and many other things.

I agree with "letmetellu" but you can cause yourself a great deal of trouble if you overcharge a system and money (ie electric bill and additional svc.). Consider hiring a local co. to do a "maintenance" this is often cheaper than a svc call and you will very often be informed of any existing problems.