You CAN say these things. The meanings of some are a bit strange though.
#1
It is very common to say "Do YOU happen to know what it is?" Using the first person seems odd though. It means something like "Can I by accident (or by coincidence) know what it is?" That sounds odd because you already know what you know, so why would you ask such a question?
#2
This is OK, but you should use "could" instead of "can". Other ways to say the same:
"Might I go there?"
"Can I perhaps go there?"
#3
This is OK but might not be the best way to say what you want to say. What are you trying to say? There are several possibilities:
"Is it possible that I might meet the person?"
"Might I run into the person?"
"I want to meet the person. Can that be arranged?"