John Gill Commentary Mark 13:3

"And as he sat on the mount of Olives over against the temple, Peter and James and John and Andrew asked him privately," — Mark 13:3 (ASV)

And as he sat upon the Mount of Olives
On the east of Jerusalem:

over against the temple :
where he could have a full view of it; the eastern wall of the temple being lower than the rest; (See Gill on Matthew 24:3).

Peter, and John, and James, and Andrew, asked him privately ;
apart from the rest of the disciples, they being, especially the first three, his favourites, and very familiar with him.