Tell people what you don’t know. No one knows everything. There’s nothing wrong with this. You can build trust by explaining what you don’t know. This implies that you do know what you’re talking about when you address a subject. Acting like you’re omniscient reduces your trustworthiness.
Figure out what you don’t know. If you want to take things to the next level, use Google or whatever it takes to find the answer to what you admitted you don’t know. This shows your ability to do research and to follow through—both powerful components of trustworthiness.