In a regular ko, the board position will not repeat because there has to be an intervening ko threat. It is easy to keep track of because it happens immediately, although even in pro games, sometimes people have what is called “chakgak” in Korean, an “illusion”, and will make a mistake and take back the ko without a ko threat. In this case, the game is lost, regardless of whether one is winning, or it’s at the end. This happened once I saw in top pro competition. In a friendly game, I think it’s okay to just say, wait, I just took it, you need to make a ko threat first.
In “unusual” ko positions, imagine something like there are three related kos keeping groups alive. Again, it’s going to be clearer than it sounds in actual play, because the ko threat of taking a ko is going to be pretty clear and happening immediately, that is what is keeping the game in a repeating loop. It is extremely rare. For example, both sides are going to have to keep the kos going, one side can’t just connect a ko and still be on the road to capturing the group. If neither side wants to connect, you can just say it’s dual life, and there are no points there, keeping in mind that we aren’t suspending capturing and basic ko rules, so it could be considered a source of endless ko threats, for example. This all sounds extremely complicated, but you will know, if you know the last move played and the basic rules, what’s legal. Whether a legal move is a good idea, is something you’ll have to figure out, and everyone has trouble with that.
When I was just starting, I used to worry if these complicated rules would come up just when there were a few kos around the board, for example, in the end, when there’s a lot of “half-point” kos that you are filling. Imagine that you have three half-point kos, for example. You take a, the other takes b, you take c, the other takes a, you take b, the other takes c, you take a, etc. etc. Then I realized in order for this to happen, one side has to be able to capture two of the kos from the starting round and the second round, which is impossible. Again, sounds complicated, but in real life it’s immediately visible that you can’t capture a ko that you’ve already captured, so the board position cannot repeat.