after some diagnosis I have to replace an ignition switch on my 99 sonoma.
I have the switch but when doing research, many sources indicate that when plugging the new switch I have to ensure it is in the off position...
how do I know which is the off position on the switch?

All the way counter clockwise should be ACC, one click clockwise should be off, one more click CW is run, and all the way CW is start.

It should be in off when you get it and do not move it around from position to position as it can damage it if you do so before installing

In the 1998 and later Sonoma, S10, Blazer, Bravada, etc you actually want to repalce the switch with the key in the ACC position. It aligns up easiest that way. Confirm the position of the switch you pull out matches the switch you are putting in. By going to the ACC position, the switch is in its farthest position, so hard to make a mistake in position during replacement.

I have a 98 jimmy and I lost the keys. How do I replace the lock and cylinder with out the old key?

It is much easier. Just go to GM dealer with VIN and they can cut a replacement key.... Typically 40 or so dollars.

I lost my keys while in Afghanistan, and had a buddy go to dealer with my VIN and they cut the key for him on a 1997 Bravada. He sent the keys to me at FT Bragg and when I returned, open the envelope with the dealer cut keys and Bravada started right up.