Which direction should the slit in the bishop's miter face


It doesn't matter; it's all personal preference. Same with the rest of the pieces (especially the knight).
It doesn't matter; it's all personal preference. Same with the rest of the pieces (especially the knight).
Well, some of my opponents insist that the knights should always face the opponent and not sideways.

All horses should face rightward from White’s perspective, and all bishops should face leftward from White’s perspective.
*In my opinion.*

All horses should face rightward from White’s perspective, and all bishops should face leftward from White’s perspective.
*In my opinion.*
Nonsense. The Knights should face the center.
In other news...
The King of France (I forget which one) was playing chess with one of his courtiers. After a few minutes thought, the courtier reached out, picked up his Knight... and let out a loud fart. The King leaned back in his seat and raised an eyebrow. The courtier (thinking fast) said "Sire, my cavalry will not advance unless they hear the trumpet call!". The King gave him a cool smile to acknowledge the clever save... but he didn't play chess with that particular courtier again.

It's personal preference. Though usually it's the knights that people adjust - not so much the bishops.
Carlsen, for example, often sets his knights so that they face toward each other.
Caruana, on the other hand, often sets his knights so that they both face to the left.
You could do the same with the lines in the bishops, too, if you like. It's up to you.