If that is a catapult launch, I would expect them to test a drone first instead of manned aircraft for safety reason, so most likely a green primer painted GJ-11, then they will likely proceed to launching J15T. I don't think J35 will be EMALS launched at this stage, if all goes well, may be at latet stage of this sea trial.
J35 prototype is too valuable for initial live testing of the catapult. This sea trial most likely is centred on the verification on the functionality of the catapult itself and not the aircraft. There is no hurry to test J35 on Fujian as yet.
J35 will be test launched when the tests on ship borne catapult passed the requirement. Remember that previous test results of land base EMALS may not be the same as ship borne EMALS.
The green primer could be anything: KJ-600, J-15T, J-35, GJ-11J, they all come in green primer fresh off the line.
Personally I don't think it changes anything whether it is a J-35 or not, or whether it's a J-15T or a GJ-11J or whatever -- the catapults themselves should've already been thoroughly tested at sea conducting test launches underway without any loads, and they've already done dead load test launches at port.
At this stage what they should be doing isn't testing the EM catapults themselves, but rather testing them with aircraft, and the aircraft that are to be integrated with the ship, namely the above aircraft types mentioned.
The only reason why they might not test J-35 yet, is if J-35 is aerodynamically not at that stage of risk reduction in its testing, but I have a feeling it probably should be there.
Putting it another way, whichever aircraft they choose to test on CV-18's catapults right now is probably less related to the reliability of the catapult (which should be about as reasonably known a factor as it can by now), and more related to whether the aircraft they want to test are sufficiently aerodynamically and structurally verified for testing at sea
Remember, they should've all had land based catapult testing already as well, before they go aboard the ship.
If anything, conducting the first couple of sea based catapult tests should be more of a formality than anything, because all of the requisite elements of "launching an aircraft from a carrier's EM catapult at sea" should've already been vigorously tested and risk reduced in its constituent parts.
Or still another touch-and-go
I agree, this is also a likely (if not more likely) option, simply because waiting for a confirmation of a catapult launch of an aircraft imo should be best done with good quality imagery/footage.