With the Golden Veto Pass you can replace a player once the selections are made. So you can't block someone specifically but you can replace them if you want to.
Here is what is written in the Cave of Wonders about your power
Golden Veto Pass: When you are granted this power, it means you can use it to replace someone who was picked to play in the Power of Veto. You can replace any of the 6 players, even the HOH or the nominees with the Golden Veto Pass. It can only be used once & has to be used before the final 6. This power IS transferable.
Subject: Power 
