In Troyes, how do use Chivalry and Joust as part of a VP engine?
Chivalry by itself is difficult to be a good VP engine. Its strength lies in that you can distribute the cubes anywhere so it can help you gain fight events regardless of the typical dice color. As you noted in your question, the challenge with Chivalry is that it it gives you a cube for each red die you have left after the cost is paid. Since you typically lose 2 to 3 red dice just battling events, it can be hard to effectively defeat events this way.

As the previous answer suggested, this can give you some good end game points if you spread out the cubes and get the 1 VP credit for having a cube per event card at the end of the game.

Where I've seen Chivalry used extremely effectively is with the Captain which gives you that same bonus when activated. If you have a good number of cubes spread out on event cards and activate the Captain multiple times you can have a powerful VP engine.

Joust took me a bit to fully understand, but this one can be a very good source of VPs. The key to remember is that you don't need to have the highest # of red dice (after you've paid to activate it), but instead the highest total of pips on the red dice you have left. This means that if there are 2 red dice left and you have one that has only 1 pip and an opponent has one that has 3 or more pips, you can buy that die from them and activate Joust and score your VPs. Also b/c it only costs 3 to activate, this is one that you can activate multiple times fairly easy.

One last thing to consider is the VPs you get for being first or second to purchase. Chivalry only pays 2 for the 1st player and 1 for the 2nd player. Joust pays 3 for the 1st and 2 for the 2nd. So if Joust first position is available and you can get the dice to make it work, I'd strongly consider it.