The actual meaning depends on the context. It can be:
* A question: "What am I doing to you?", perhaps in a playful or apologetic way.
* A statement: "This is what I am doing to you", implying a particular action or effect.
Here are some examples:
* "Que je te fais?" - "What am I doing to you?" (Asking why someone is upset)
* "Je ne sais pas que je te fais." - "I don't know what I'm doing to you." (Explaining an unintentional effect)
* "C'est que je te fais, tu vois." - "This is what I am doing to you, see." (Explaining a specific action)
The best translation will depend on the specific situation and the speaker's intentions.