Hi,
With the help of youtube videos Grant Abbitt (beginner exercices part9), i decide to create the full pieces of chess game.
I have some questions :
I think i have the same problem with the rook.
Sorry for my english and i’m relatively new with blender 
Regarding the bevel on the bishop, you first have to apply the boolean modifier. After that, the geometry is there for you to bevel, so just select in edit mode, and bevel away!
Regarding the distortion, that is because you have smooth shading enabled. Smooth shading rounds out the existing vertices, so if you want to have finer control over the appearance of the shading, you need to have that extra geometry. Maybe try to insert an edge loop in the middle and see how that affects the look!
Good luck 
You can also use auto smooth, where a mix of smooth and flat shading is applied depending on the angle between connected faces.
The problem when i apply the boolean is the bad topoloy.
The correct follow is retopology and bevel the contour of gap ?
From what I see even the low poly versions look nice with the materials on. There might not be a need to go for subdiv.
see this tut
happy bl
