Can I trade traded pokemon?

You cannot trade traded Pokémon. Each Pokémon can only be traded once.

No matter who you trade with, a traded pokémon cannot be traded again to anyone.

Poor IVs obtained following a trade cannot (currently) be changed. A traded mon may still have value to you based on who traded with you, location, time stamp, etc. It's CP may make it a good candidate for the Great or Ultra leagues.

It is possible that in the future they will implement the ability to trade a pokemon if it was traded over a year ago, or something like that. But there is no guarantee of this - it's simply that if that were the policy, no one would have a traded pokemon that qualifies yet.

It's fairly obvious why they have to do this. Even if you could only trade once a month, players would get together and swap traded pokemon around, taking the ones that get great stats out of the trading pool.

So, as of now, no, traded pokemon can be sent to the professor for candy, or kept, and that's it. Might change in the future, might not.

Pokemon can only be traded once in Pokemon Go. So you can't get back any pokemon that you traded away.

You can however send a traded Gen1 pokemon to Pokemon: Let's Go on the Nintendo Switch. That is also a one way trip though and can not be sent back to Pokemon Go.