The scoring system of the Digger XP is similar to the original Digger. Here it goes:
Emerald
25 points
Eight consecutive emeralds (octave)
Extra 250 points
Gold
500 points
Killing a Nobbin or a Hobbin by shooting or hitting with a bag
250 points
Bonus
1,000 points
Eating a Nobbin or a Hobbin (In bonus mode)
200 points for first, 400 for 2nd, etc. (doubling each time). Still 250 for other methods of killing, though.
At every multiple of 20,000 points you get an extra life.