Fill cells in Sheet 1 with value on Sheet 2 - return value from same exact cell on Sheet 2

Sheet 1 Cell A1 input is "?" when entered, the cell should fetch/fill with value from Sheet 2 cell A1 (same cell only) 

If Sheet 2 Values are

And on the empty sheet 1 input of "?" on any of the cells that has value in Sheet 2 should populate. I have been trying various formulas but can't seem to make it work.