What’s the best way to get there by train from New York Penn Station?

The 2 or the 3 trains are your best bet. Take either one to the Atlantic Avenue-Barclays Center stop. Take the escalator upstairs and you'll be right in front of the building. Check with the mta website, before leaving, for possible service disruptions >>> new.mta.info

Yes the 2 or 3 train

Probably q like stated above the station is right there

Yea. Just take the train. to the Atlantic Terminal. When u go up and out to the street just turn left Nd walk to the corner. Ur there