There are 8 Diglett to find in Challenge Road.
Alolan Diglett #1

When you enter Challenge Road from Brawlers’ Cave the Diglett is near the entrance to your right by a rock.
Alolan Diglett #2

When you enter Challenge Road from Brawlers’ Cave the Diglett is at the nearby cliff edge by some bushes. When you enter this area you’ll straight away see a Pokemon Den. Thats the cliff you want to head to.
Alolan Diglett #3

When you enter Challenge Road from Brawlers’ Cave go up the first ramp to your left. Once up turn right and follow the narrow path through the tall grass. The Diglett is hiding just after the tall grass by the edge.
Alolan Diglett #4

When you enter Challenge Road from Brawlers’ Cave go up the first ramp to your left. Once up turn left and go down the first set of stone steps. The Diglett is hiding in front of a rock and some bushes by the edge to your right.
Alolan Diglett #5

When you enter Challenge Road from Brawlers’ Cave go up the first ramp to your left. Then go up the next ramp in front of you. Then turn right and go up the ramp with a rock on it. The Diglett is hiding behind the Pokemon Den by the edge.
Alolan Diglett #6

When you enter Challenge Road from Brawlers’ Cave go up the first ramp to your left. Then go up the next ramp in front of you. Then turn left and walk through the tall grass. The Diglett is hiding behind the rock by the edge.
Alolan Diglett #7

Fly to the Tower of Darkness. The Diglett is to your right by the edge. Alternatively, when you enter Challenge Road from Brawlers’ Cave go up the first ramp to your left. Then go up the next ramp in front of you. Now go up the stone steps in front of you. The Diglett is to your left by the edge.
Alolan Diglett #8

Fly to the Tower of Darkness and go down the stone steps. The Diglett is by the rock on the sandy slope.