So if you don't already know, "sealioning" is a term for a type of bad faith behavior where someone repeatedly asks for information or evidence that they're not actually interested in. It's a form of trolling.
For example, a young earth creationist might go around saying something like, "Can anybody show me proof of evolution? I keep asking people, but no one will answer me."
Then well-meaning people come and and provide resources. The troll, who of course isn't actually interested in learning or changing their mind, will just keep acting like nobody's answering their question, and keep demanding answers. It's frustrating and exhausting.
A big sign that you're being sealioned is demanding information that's incredibly easy to find. Now of course, people sometimes genuinely just don't know where to find certain information that most of us take for granted, and sometimes people are just lazy and treat random Internet strangers like their personal butlers. (Having a pinned post with a FAQ will take care of most of these people, btw.)
What gives a sealion away is their refusal to accept and engage with provided resources, and their favorite lie, "I keep asking, but no one will answer me."
Think for a moment: how likely is it that someone went around asking a bunch of biologists or at least biology nerds for evidence of evolution, and no one gave them anything? Does it seem that likely that no one gave them any links or made any book recommendations? Does it seem likely that a bunch of people who really love talking about biology just suddenly clammed up around this person for no reason?
Trolls will sealion over anything, especially hot political topics. For example, they've been sealioning with JK Rowling's transphobia, asking for evidence that she ever said or did anything transphobic while claiming no one ever answers them when they ask. Trolls have been sealioning for Donald Trump for years now, pretending they just don't understand why people are so worked up over Trump, and that nobody they've asked will give them a real answer.
Again, ask yourself: how likely is it, really, that someone on Tumblr Dot Com can't find a single person who can tell them what these people have done and said that have so many people displeased with them? And do we think that this person who is supposedly soooo interested in seeing what all the fuss is about, never once tried Google or something?
Seems pretty unlikely, when you actually stop and think about it. In fact, it's a pretty obvious lie, because we know damn well that lots of people are more than happy to explain why they don't like Trump and Rowling, and any determined person could find the information they want in like five minutes on any search engine.
Sealioning is troll behavior. If someone is sealioning, they are a troll. It's that simple.