Please help I have beat the elite four,But the sky pillar doesn't show..

Ok, go to Mosdeep City and Surf South until all you can surf to is rocks. Then just Surf West, you'll arrive in Pacifilog Town. Leave Pacifilog Town to the NorthEast and you'll see Sky Pillar.

Did you do the Regi Cave thing yet? Otherwise then they obviously aren't there.

Ok go to pacifidlog and then surf east. Stay towards the top of the rocks and there should be an opening there. Take the mach bike you will need it to go over the cracks.

You probably can't find it. I believe that if you went to Pacifidlog, and surfed east until you came across a boy and a girl looking in opposite directions (one looking up, the other looking down), surf north through an opening in the boulders, around a path bordered by boulders, you'll come across it. Make sure you have Mach Bike on ya, for there's those hole traps which will cause you to fall if you put your weight on them.

As for the Regis, did you unlock them? You need a Relicanth in front of your party, and Wailord in the back, a Pokemon that knows Dive, and a Pokemon that knows Dig. Surf west from Pacifidlog, and into the current, keeping a little close to the bottom of the route as you ride the current. About 2/3 through the route, there's a nine-square diving hole. Once you are there, use dive, and when you hit the end of the trench down there, you'll see a rock with Braille on it (it says "Go up here" or something like that). After you read it, use Dive. You'll be in a cavern. At the top of the room, there's some more Braille. After you "read" it, use Dig. Go through the hole and when you walk to the center of the room, there's going to be an earthquake, three sounds, and a message saying three doors opened up somewhere. You've just unlocked the Regis. You can go ahead and exit now, so you can attempt to capture them.