What to do with Apple Cider Jelly?

Try it as a glaze for pork ribs. Rub your ribs with a dry rub or just salt and pepper. Cook then at the last 15 minutes, glaze with the jelly until it caramelizes. You can also punch up the heat by warming the jelly and adding fresh chilis then glaze the ribs with this.

You can warm it and use as syrup for anything you'd put maple syrup on. What you have is apple cider that has been boiled down until the pectins are ready to hold it in the jelly form. Unopened jars should last as long as other jellies. It's really precious stuff.
My mother-in-law made a cake icing from beaten egg whites and apple jelly, but I don't have the recipe (too late now). You may be able to do something similar -- it was a favorite.
I wouldn't want to add strong flavors to it. Let the concentrated apple flavor shine!

If it's fairly mild, you can melt it and use it to glaze a fresh fruit tart.

Assuming it's not too heavily spiced, it would be great in a savoury pan sauce - thinking pork, duck, chicken, turkey. Often apple jelly or red current jelly is used in this way to give a pan sauce body & a touch of sweetness.