The NES version of Hook is a pretty terrible game, but if you absolutely must see the ending, I have some good news, I guess.

First, go to the title screen.

Then grab Controller 1 and press Right, Up, Up, Down, Down, Right, Left, Up

Done right, you'll hear a sound, then hit Select to see the ending... which really just consists of two screens of text with a Tinkerbell flying around in front of them.

Or, you could just start the game. If you do, you can use the compass to point to a stage and hit the B button to move around on the map, and the A button to play any stage you like.

But since you've already seen the ending, I'm not sure why you'd want to do that.