Only what they personally have dialed from that gate previously.
Only players in your tribe can get your gate list of gates you have placed.
At least that's how it is on my servers.

Add a shield to your stargate. Then unauthorized players will go splat. :)

Any non public stargate has a list of addresses dialed, so any random player can go up to it, see what address was dialed before and enter that address and port to your base.

is there a way to make the gates private? there is virtually NO security with these then! I have one inside my base! you mean random ppl can port right into my base by reading the list of visited gates on the left side? I surely hope this is NOT as intended and I am reading this wrong! Can someone clarify plz?

Put a shield on the gate when you log off and anyone will take over 1 billion damage when they try
or, as I do it, I put my gate room as my dino storage pen and place turrets, if they don't die to the turrets, one of the dinos will eat them

another tactic is always redirect your travel to the fishing village (if enabled) and then your home gate. fishing village is a public gate and won't store the address