Peel the onion, cut it in half lengthwise, and cut into very thin slices. Put the slices in a bowl, cover with the lime juice and apple cider vinegar. Sprinkle in the sugar and salt. Stir and toss to dissolve the sugar and salt and set aside.
Shuck the corn. Use a sharp knife to cut off the kernels (pro tip: set the tip fo the cob in a big bowl and cut down so the kernels drop into the bowl).
Remove the stems from the jalapenos, cut them in half lengthwise, remove and discard the seeds, cut them crosswise into very thin slices.
Toss the corn, onions with their pickling liquid, and chiles together—the pickling liquid acts as the dressing.
Chop the cilantro and toss it into the mix.
Crumble the cotija over the top and serve.