Stand in front of the door and have a pokemon use the HM move CUT. The door will break and you are able to enter the cave.
use cut
If the scientist is blocking dotted hole go to four island and go into icefall cave in there find HM7 which is waterfall use it to go up the waterfall in the cave then go to the ladder you will find some rockets and lorelei beat the rocket then leave to six island he shouldn't be blocking dotted hole anymore now use the move Cut on the door to open it.
To open the dotted hole, use Cut at the entrance and the door should open. he is so right it does open
dotted hole is on the south side of six island. (the sapphire is in there) a little extra info: dotted hole does have braille in it.
Beat all the rockets in Island four's Icefall cave
The Dotted Hole in on Six Island. You go toward the right of the Poke Center and walk south. Follow the path which is somewhat like a maze. Use the HM move CUT to open the door and you will find a SAPPHIRE in that cave.
Mt ember and dotted hole.
You can find the sapphire in the dotted hole cave on six island to find the cave go to the southern portion of the island, use Cut on the door to open it then fall down the hole in the cave then fall down the holes in this sequence: up, left, right, down.
You need to use Cut on the metal door
Go to four island and go in icefall cave find HM7 in here which is waterfall use it to go up the waterfall in the cave go to the ladder then defeat the rocket then talk to lorelei go to six island and go to dotted hole the guy should be gone now use Cut on the door to open it.
the dotted hole is opened by using cut when you stand in front of the door
Its in dotted hole not lost cave, in dotted hole fall down the first hole then you will see four holes fall in them in this order: up, left, right, down then take the sapphire.