Poor thing. You're going to have to change a few things, a couple now, the rest after it blooms.
It needs more sun and water right now. Is it outside? If it's indoors it probably needs a full, unfiltered southern window, but I've never heard of growing lilacs indoors, not sure it's workable.
Feed it with a balanced liquid fertilizer according to the product's directions, not stronger. Plain old regular Miracle Gro is fine. Do that now. DO NOT use a dry organic product designed for use in outdoor garden soil; the potted environment will not break it down to make the nutrients accessible to the plant.
Then wait for it to flower (if it does) and fully leaf out. While you're waiting, read about lilac care. Then you'll want to prune it properly and repot in good, well draining potting mix. The existing pot looks a bit big; you might want to downsize an inch or two. Check in here in a couple of months with an update about whether it bloomed and we can help to with future steps.
