Q1. Do you need to prep for Tarot readings? Or does Tarot always reveal cards that are pertinent/meaningful to the topic at hand?
I like to clear my mind and avoid distractions when I'm giving a reading, but I think that's more about professionalism. When I'm reading for a client, my attention should be entirely on the task at hand, and not on any personal thoughts of my own that aren't relevant to the business of reading.
As to whether Tarot cards are "always" relevant, my personal stance on this is that any of the 78 cards could come up in a spread and there would be some meaningful way to interpret them in the context of a querent's question. So in that sense, I suppose my answer would be yes, the cards are always relevant, but that's really a lukewarm, halfhearted sort of yes.
*Whether or not you relax your mind and think about the exact question before you flip.
The cards are already in the order that you've shuffled them in, and by the time you get to the point where you're flipping cards, the same spread is going to come up regardless of what you're thinking of. Now, that said, I think that if you're focused on the reading, you'll probably have an easier time of
interpreting the cards that do show up, but it won't have any effect on which cards turn up where.
Some readers believe that you should focus on the question while you're shuffling, and that doing so somehow arranges the cards so as to better answer said question. I personally don't hold this view, but if you find it helpful, you might want to give it a try.
Q2. If you want to ask about something regarding a particular person, but only think about the person when drawing a card, does the card always reflect the tarot's opinion on your unmentioned query? Or something else...?
A large part of this depends on your reading style and personal beliefs. I tend to interpret cards in a reading as centered on my querent's behaviors and beliefs, so that I'm more likely to read the "Person X" card in a spread as "Querent's relationship to Person X" or "Querent's views of Person X". Other people may read it as an objective description of Person X's personality, or something else that's tangentially related. Ultimately, any card in a reading could easily mean a variety of things, and the best thing you can do is sort through and look at each of the possibilities before you decide on what you think the best one.
Your question was a bit difficult to understand, so I hope I answered appropriately. If not, let me know.
Good luck with your Tarot explorations!