Self-Identifying Coordinates
Dyalog APL, 5 3 bytes



⍳⍴⍨


-2 bytes thanks to FrownyFrog

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⍳ gives all the indices given the shape of an array. e.g. 2 3.
⍴ reshapes the right arg to be the size of the left arg. ⍨ makes both be the right arg.