This is an impossible question to answer, but it is definitely a case of quality over quantity. Instead of trying to log something every day, which may be quite meaningless, set aside some time to think deeply about an experience. Start with what happened, then consider why, how it made you feel and what you would do differently next time. Keep those sorts of questions in your head. If something notable happens, then these should trigger your thoughts. If it is just a normal day working towards a distant goal you may not have anything to reflect upon, and that is fine.