Shortest path for a chess knight
APL (Dyalog Classic), 55 bytes

{⍵⌊d⍴1+⌊/¨⌷∘⍵¨¨a/⍨¨Ö↓2=×/↑|∘.-⍨a←,⍳d}⍣≡0@(⊂⌽⎕)⊢9⍴⍨d←8 8

{⍵⌊d⍴1+⌊/¨⌷∘⍵¨¨a/⍨¨Ö↓2=×/↑|∘.-⍨a←,⍳d}⍣≡0@(⊂⌽⎕)⊢9⍴⍨d←8 8
                                       0@(⊂⌽⎕)⊢9⍴⍨d←8 8 ⍝ create an 8x8 grid of 9s with a 0 at the start position
                           ∘.-⍨a←,⍳d                    ⍝ all differences between coordinates
                     2=×/↑|                             ⍝ is 2 equal to the product of the absolute values?
               a/⍨¨Ö↓                                   ⍝ filter where true (finds knight moves)
          ⌷∘⍵¨¨                                         ⍝ index into the board
     1+⌊/¨                                              ⍝ 1 plus the minimum (finds minimum distance)
   d⍴                                                   ⍝ 8x8 reshape
 ⍵⌊                                                     ⍝ the minimum of the new and old moves
{                                   }⍣≡                 ⍝ apply until converged (minimum distances found)

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