I wouldn’t chance using jb weld in the tank. But you can try reef epoxy putty. But I tried epoxying wet live rocks together years back and it eventually broke off after a few months. Also any epoxy will cause your skimmer to go bananas.
I my self use acrylic rods and super glue gel if the rock is wet. What I do is take an 1/4”acrylic rod and cut a 4-8” piece. Then take the 2 rocks and see how I want to make them stick together. Then take a 3/8” masonry drill bit and drill the hole deep enough to for half of the rod to go into the hole. Then put a shoot of super glue gel in the hole and a nice little glob around the hole. Then put the rod in the holes and glue the rocks together. Then I’ll take a little sand or gravel and sprinkle it over the glue that has popped out of where the rocks meet. Yes the rocks will need to be out of the tank to do this.
This is how I did my center rock piece