How can I get user-defined inputs?

Iv’e been wondering if I can get the user-defined button values and use it in some parts of the game. For example, if player is near to a pickable object the GUI label would say

Press [the user-defined button] to pick up [pickable object name]”.

Iv’e been seeing it in most games.
Any ideas will be appreciated, thanks and pardon me if I’m a novice.

This all depends on how you implement re-defining keys by the user. For example if you use KeyCodes:

#pragma strict

var jumpKey = KeyCode.J;

function Start() {
	Debug.Log("Press the '"+jumpKey+"' key");	

function Update() {
	if (Input.GetKeyDown(jumpKey)) {
		Debug.Log("Do a jump");