Press F3 in the world — a text column will appear on the left. Coordinates are in the first lines: XYZ — the exact location, Block — the block you are standing on. Press F3 again to close the debug screen. On laptops where the F-keys are occupied by brightness and sound, press them together with Fn.
X — east (+) and west (−), Z — south (+) and north (−), Y — height: sea at 63, world floor at −64. All debug screen keys are on the page F3 Screen.