How to change wiring in outdoor electrical junctions filled with gel?
It looks like something that used to be done for pool niche lights or landscaped fountains and ponds. This was a non-conducting waterproofing gel that was used to prevent corrosion and power leakage in wet location areas. It was usually applied in a time, post new GFCI and grounding requirements. I haven't seen it used in quite a while. 

If you are trying to reuse the circuit in a newer application. You really need to verify that it is still active. Then you need to verify if the conductors and cabling are working properly.

Basically do everything necessary to upgrade the circuit to current wet location codes. Even if it means replacing the entire circuit. It is important to remember that you are dealing with a type of circuit that has a high potential for electric shock (electrocution). So it is important to follow the strictest protection codes.

Hope this helps.