So, when you write a hook for a rap song, the key is to make it very conversational, meaning that this is how people express themselves in your social circle. And the way that you make sure that you are in alignment with how people actually speak, is making sure that you are a good listener.
When you're hanging out with your friends, Biggie Smalls was notorious for this, no pun intended, what he did, and he said this many times, is he paid attention to what his friends were talking about. And by paying attention to what his friends were talking about, he may grab something that was catchy, or a hook, that could hook people in and made that the title of the song, or made that the title that was really highlighted in the chorus, because it was something that hooked his attention.
And that's the way you write a hook.The key is not to try to be super-duper imaginative. It's to really pay attention to what's going on in your social circle and how people talk. And then you grab that hook, or that slang, or that terminology from your friends, from the way that people talk in your social circle, and that will be your hook.