What we know:
The lava lamp was found to contain water, 38% by mass; chlorinated paraffin, 36%; low molecular weight polyethylene glycol, 13%; kerosene 7%; and microcrystalline wax, 6%.
Lava lamps flow optimally at 45-50 C.
The wax contains paraffin wax, a mineral oil such as ondina 17, carbon tetrachloride, and petroleum jelly.
The liquid contains glycerol ethylene, glycol, polyethylene glycol or propylene glycol (30% of total volume).
Here are the two vintage patents for the lava lamp formula that have a hint about what the formula might be.
What we dont know:
The correct mixtures of the above chemicals.
This discussion goes into detail about the formula.