pardon if the answer is clear somewhere else, though I'm very new to the platform...
are there specific guidelines published anywhere on the protocol for posting others' content?
i.e. if we're sharing content we didn't create, what exact details must we include to specify it is syndicated and not original content?
if there are such guidelines, where are they to be found?
You're asking the wrong person about guidelines. I generally don't follow them if they exist and they are usually created after I've done something others find offensive. Regardless, this is a blockchain and there are no rules. Make your own rules and see what works for you. This is a popularity contest. We could post the same thing and you could make thousands, while I would be downvoted into oblivion. If you want to make $$$, pander to the whales! Just don't point out the obvious pandering publicly or you will not receive the whale love. Let me be your living example of how not to behave on Steem ... if you value money over integrity. :)