I would love to help, but think it's too vague. Kinda been stumped if this is a philosophical riddle or not.
I guess I can try, but it may not be what you're looking for.
So the first half, let's dissect that. "What should I do in this life if I could not tell you anything else?". Well, the best way to figure out the question is by inverting it. "What should I not do in this life if I could tell you anything?". That would mean that if you could tell me anything, what would you avoid doing? I still am confused, so let's switch perspective. "If I could tell you anything what shouldn't I do in this life?". If I weren't afraid to let you know all my deepest darkest secrets, what am I doing that I shouldn't be doing? So let's switch it back to fit the original question. "If you were scared to tell me all your deepest darkest secrets, what aren't you doing in life that you should be doing?"
I'm sorry, but your question can't be answered. You're missing the essential part that makes it all work. What could you tell us? I don't know what is missing from your life to tell you what's missing. So to answer your second question, no this question cannot be. Your question cannot exist without proper context.