"How" is a tough question. "That" we will know them is easier to see. In Jesus' story of the rich man and Lazarus, they knew/recognized each other.

John, seeing Jesus in Revelation ch. 1 said he saw one "like unto the son of man," meaning that he recognized Jesus, even though He was very different in appearance than their last meeting. When Moses and Elijah appeared on the Mount of Transfiguration, Peter and the others recognized them, even though they'd never met. We have some kind of identity in heaven that reflects our identity on earth, but in a perfect, incorruptible, yet recognizable way.

Ask me again in 1000 years. I'll have a better answer then! :-)