Cool, initially I was hoping to squeeze it into 8 Lines, though had to go the full 10, still managed to get your Program Remarks in, though had to go on the same line.
Apart from the Grid, everything else is PRINTed in using Redefined Symbol DATA (240..247), TAG & TAGOFF, using a Control Code to switch on the Graphics Write mode (prevents damage to the Grid). The initial Knight is Placed and Filled in using Redefined Symbol DATA (248..255). I would have got away with Drawing the Knight shape as your example shows, though needed to extract the Shape of the Knight to work out where the FILL needed to occur. Once I had that and worked out where the Number '1' was placed, I had the shape to Redefine Chars 248 to 255. In your version I noticed the FILL didn't reach behind the lower half of the Knight and the Number '1', though decided to hit that area anyway.
With all the Redefined Characters though, I had to Compact it right in to make it fit, CHR$(0) is used quite a bit which Cursor Copy cannot extract and CHR$(128), which Cursor Copy confuses as CHR$(32) needed to be defined as z$ and b$, while Redefining the Characters (hence the reason for their presence in those initial lines).
Cheers, Ross.