I’m making chocolate chip cookies and the recipe calls for “buttermilk biscuit and baking mix.” I don’t have any of that, nor do I really know what it is, but I was wondering if I could replace it with “Aunt Jemima’s Pancake Mix.” Or, if that doesn’t work, whether plain all-purpose flour would be better. Cooking gurus, please help! Thank you!

USE FLOUR!!! You don’t need biscuit mix for cookies.
Traditionally you use all purpose flour, for the nice texture.
the buttermilk biscuit and baking mix is better known as Bisquick here in the USA. I think it is something else across the pond.
Yes, you can use Pancake mix instead. You might want to use a bit more all purpose flour. After mixing up your cookies, put just one cookie on the cookie sheet and bake it according to instructions. If it comes out right, bake the rest. If it doesn’t, like it spreads all over the cookie sheet, add more flour and try one cookie again.
Yes, that is time consuming, but saves lots of aggravation in the long run.
What they want you to add is something like Bisquick. Bisquick contains flour, salt, baking soda, and oil. To make pancakes with it, you add milk and eggs. If the Aunt Jemima pancake mix is the kind where you just add water, it probably has powdered eggs in it. And, this might affect the consistency of the cookies (might make them more cakey).
You could try it. Just expect that they won’t have the same consistency as if you used the Bisquick.
And, don’t just use all-purpose flour. You need the salt and baking soda to make the cookies rise. Without them, your cookies will be flat and dense.
I would only suggest using it if it is the kind that says “Complete”. That means all the other ingredients are already in the mix. If it is the kind you need to add egg and oil to then it won’t work as a good substitute.
If the flour mix calls for a little milk then just add buttermilk instead. Use all purpose flour or Bisquick