How would I can a jar of homemade harissa?

No you cannot can harissa without first cooking, and chefsusie has provided a most useful link. The recipe in the link adds acids so the harissa can be safely canned, so it is not a traditional recipe. I agree with susan g regarding freezing. That way it will be safe and you will have the flavors you want. If you want to start canning recommend you get Ball Book of Canning and Preserving (amazon and most stores). Also the National Center for Food Preservation http://nchfp.uga.edu/ has amazing education.

Other than using a chemical preservative, you can't really preserve the harissa without cooking it (e.g. water bath or pressure cooker method). I would go with the advice to freeze it. Or sterilize your jar and lid, pack the harissa hot and keep in the fridge. This way it should last a few weeks.

I would freeze instead. That way, you can open, use and return to the freezer, for constant access.

Do you have any experience Canning? Do you have a metal cage for the pot? You cannot sit glass jars on the bottom of a pot. Also you need canning jars. Not regular jars. I recommend getting a basic canning book by Ball. They cost around 8-.

Here is a recipe adaptation: for Harissa that has tomato: (an acid type food) can use a bathwater canning. Other types of foods cannot be canned this way. They need a pressure canner.

http://www.blazinghotwok.com/2011/08/i-will-remember-this-summer-as-summer-i.html

To store for later? To ship somewhere? I usually just put mine in a clean jar (no boiling necessary just the dishwasher) and it keeps in the fridge for about a month.