'Wanna' is a slang term that can be found in casual conversation among peers (usually kids, teenagers, and sometimes young adults), therefore is not 'proper' English per say, though it does get the point across. It is in good practice though, to stay away from "wanna" in general since it may form bad habits in your English language learning. Now both sentences if made grammatically correct by using the phrase "want to" instead of "wanna" convey different ideas. 1. "What do I have to do If I want to keep in touch with you?" - This phrase would be used in order to ask for the actions needed to keep in touch with someone. 2. "What if I want to keep in touch with you?" - This phrase directs the subject more onto you and forms a hypothetical situation since the emphasis here is more on the "what if" part. It may help to think of the frequent movie situation of a main character leaving but still having the romantic interest trying to make contact. Hope this helped some! :)

Both of those sentences would be correct and understood if you use "want to" rather than "wanna". However, asking "How can/do I keep in touch with you?" or simply "How can/do we keep in touch?" would sound a little more natural to a native speaker. I hope this is helpful!

"What do I have to do If I want to keep in touch with you?" This is perfect. "What do I have to do If I wanna keep in touch with you?" This is not proper English. "What If I wanna keep in touch with you?" Neither is this. 'Wanna' isn't a word. Look through the pages of this site. Can you see a single native speaker who has written 'wanna'? No, you can't. So don't write it.