JOEL - First of all I can't find any scriptures that support the claim that we aren't going to know anyone, nor can I find any that say that all we are going to do in heaven is praise God. There are hundreds of scriptures that refer to praising God while we are here on earth, a few that say "praise His name forever". But none specifically say that's all we will do once we get to heaven. You might ask your friend to provide scriptures to support his claims.
In studying the Catholic Religion I have not been able to find out for myself what their beliefs are about the nature of heaven. I don't believe they have any, except for simple vague statements about "gaining the happiness of heaven" and "praising God" as your friend said. You might ask your friend what he believes it means to do nothing else but "praise God". He may or may not be able to give some kind of an answer. But it will make him stop and think; "Is that all there is to heaven?"
The Bible is actually quite silent as to what we are going to be doing once we get there. Most of what we Latter-day Saints know about life in heaven (missionary work, genealogy, teaching, creating our own spirit children and worlds, etc.) has come from latter-day prophets and scriptures. But of course that won't mean much to your Catholic friend. There are a few Bible scriptures I found that might help.

Luke 10:20
"Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice, because your names are written in heaven."

There must be a reason for our names to be written in heaven. If they are written in heaven we should have access to them when we get there. If no one will know anyone else why will we still be identified with names?

Paul the apostle wrote,
Ephesians 3:14-15
14 ¶ For this cause I bow my knees unto the Father of our Lord Jesus Christ,
15 Of whom the whole family in heaven and earth is named,

If we are a "family in heaven" as he states, we certainly will know the other members of our family the same as we do here on earth, otherwise why would he use the term "family"?

There are hundreds of instances where angels have come and appeared or ministered to people on earth or have performed or will perform other tasks as directed by God. (Gen. 19:1,Matt 4:11, Matt. 13:49, Mark 1:13, Luke 2:15, John 20:12, Heb. 13:2, Rev.14:6) I assume those angels came from heaven. Therefore, ministering to people on earth or performing other tasks for God is another thing that a person in heaven would do besides praising God.

In 1 Peter 3:19 it says that Jesus went and preached to the spirits in prison. So it sounds like learning more about the Gospel is another thing we might do when we get there.