Is there a way to query or search all symbols available for autocompletion? Not only for the current context, but everything that is memory.
Assuming you’re talking about IPython, all of the jupyter kernel messages including completion are pretty much just hanging off of the kernel object. You can compute with it like anything else: for example, to get 10 completions for everything starting with a to z:
k = get_ipython().kernel
[k.do_complete(chr(a), 1)["matches"] for a in range(97, 123)]