Find all the coordinates on a path

Slip, 2 + 1 = 3 bytes

+1 byte for the p flag. Code:

`#

Explanation:

The p-flag returns the position of each occurence of the following:

`#      // The character '#'

Try it here!

MATL, 7 6 5 bytes

This is using 1-based indexing with (1,1) in the top left corner.

oo&fh

Explanation:

o        % convert char to double 
 o       % remainder mod 2 ('#' == 35, ' '==32) makes spaces falsy
  &f     % apply `find` with 2d-output 
    h   % concatenate outputs to display x- and y-coordinates side by side

Thanks @DJMcMayhem and @LuisMendo for each -1 byte!

Try it online!

Grime, 5 bytes

pa`\#

Try it online! The output format is a bit funky, but OP has stated that it's valid.

Explanation

Grime is my 2D pattern matching language. The part after ` is the pattern, in this case a 1×1 square containing a #-character. Grime will search the input grid for a match, and prints the first one it finds by default. The part before ` contains options, in this case signifying that all matches (a) should be printed, along with their positions and sizes (p).