Good evening. I had a constant trickle of water leaking from my shower spout. Turned off the water and took the spout and knobs apart to see if one of them was the culprit. Upon turning the water back on, I still had a steady trickle, then suddenly, no water to the shower at all. I still have no water. Would this be a venting problem, possibly a sudden clog? I could hear air whistling in the water line to the spout when I took it apart. Air leak? Help please.

First you have a bad seat or washer or kit in your faucet, not knowing what kind of faucet you have or how it is made, if it is a single handle faucet or if it has two handles it is very hard to give you any advice. I do think I know what the whistling was that you heard when you turned the water off. The drip where the water was dripping out of the faucet then became a place where air could go back into your faucet as water ran out of the pipes at another point, maybe you opened a fucet somewhere in another part pf the house.
If you will describe your faucet maybe someone can help you out

I have a two knob faucet but am not sure of the manufacturer. The faucet is quite old and is quite basic. Two silver turn knobs and a spout with the shower stop on it. There is water everywhere else in the house except this particular shower.

It's possible that the faucet has become clogged with rust from galvanized pipes. It could be the line going up to the shower head too. Was your water ever orangey colored?
One way to tell is to turn on the shower (without the head) and tap the shower pipe. If anything comes out, it's most likely the pipe.