Short answer: Teach your colleague to research and learn in the way that you do.
When you find you have a colleague who seems to rely on you as being the source of all information, then something you can do is to teach them how you learn new things. For example, if you colleague asks you about a certain technology or API, then you can say to them:
Have you tried searching for that? What search terms did you use? I would suggest x search term.
Repeat this, each time they have a question that is technology specific.
Now, if they are asking you project specific issues, when you explain something to them the first time, suggest they write it down. If they then ask you the same question again, say something like:
Did you have a look in your notes you took about this? Did it give you enough information?
If they answer, "No I didn't look" then you can point them to do so, but if they say that it didn't cover it, tell them to write the new information down to add to their notes.
Lastly, if they are onboarding to a new or existing project, direct them to the documentation. It can be tech specs, design documents or even function specifications. Answer something like:
Did you check the [insert relevant document here]? What did it say? Where do you find it unclear?
Sooner or later, they will get the message that most information they require is already available and that they need to spend some time doing their own research rather than using up your time to do it. If, however, they have checked the other sources and were unable to find the relevant information, then asking you is the correct action for them to take. But make them write it down! :)