Does anyone know if I need to do a reservation for lounge before my trip if I have a priority pass for airport lounge?

As J said, no need for reservation! just have your priority pass app, boarding pass and passport. may want to carry your Citi premier miles card along just in case but from what I know they usually only check the 3 items above :)

No need for reservation. To be honest after being a fairly frequent flyer with an average of around 30-40,000 miles a year for the past 10 years I have personally never heard of a lounge even taking reservations.

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Just make sure you have your priority pass card set up and you should be good to go.