Which is better between the Knight pair and one Bishop + one Knight?

Hello.

When I first learned to play chess, I heard that having the Knight pair gives us a small avantage, and having the Bishop pair gives us an even greater avantage. But years have passed, and I never heard the words "knight pair" again.

It is generally recognized that a Bishop is worth 3.25 points, while a Knight is worth 3 points. And having the Bishop pair gives us an advantage of +0.5 points.
So the Bishop pair is worth 3.25+3.25+0.5 = 7 points. While one Bishop + one Knight (assuming you've lost the other Bishop and the other Knight) are worth 3.25+3 = 6.25 points.
But how much are two Knights worth? 6 points? Or does having the Knight pair gives us a small bonus advantage (just like the Bishop pair does)?

Basically, the question is almost equivalent to : Which is better between the Knight pair and one Bishop + one Knight?

Note : Of course I know that it depends on the position, but I want to know which is generally better on average.

Thanks in advance for your answers.

As you say it depends on position.
If it's against a bare king you can't force mate with two knights, but you can with two bishops or bishop and knight.

The points system of 1 point for a pawn, 3 for a bishop or a knight, 5 for a rook and 9 for a queen is a useful rule of thumb, but nothing more. If you start making decisions based on a bishop being worth more than a knight you're going to end up with some lousy positions where you're opponent has two wonderfully placed knights in a closed position where your two bishops have barely six squares to play with between them.

Instead of this, try to work out for yourself when a bishop is better than a knight and vice versa. The books will tell you stuff like bishops are preferable in open positions and knights in closed positions and that bishops are better than knights in endings when the position is "wider" (i.e. pawns all the way across the board), and whilst this is a good starting point it is no more than that, I've seen thousands of games where the "bad" piece suddenly became good or where two knights ran riot over two bishops in an open position. The bottom line that is tactics rule - if your opponent has a knight on the edge of the board which is helping with a forced mate in 2 then it's a very good knight indeed!

It also depends on the player. You might find that you simply prefer one piece over the other. You might not even realise this yourself - take a look at games which you lost from what looked like equal positions and see if there's a common denominator, e.g. perhaps your not very good at getting your knights onto outposts, or perhaps you fall for knight forks a high percentage of the time. If so, exchange your bishops or knights as appropriate as early as you can!