Finding question queries containing specific keywords .. please help

Hi,

I intend to create content that answers questions, relevant to my target audience, in the form of articles that cover such questions. But how do I find out ..

a) what questions are of interest to my target audience?
b) how - meaning with which concrete question queries - it searches for them?

Example 1:

Assumed, I run a recipes website and would like to find out what questions my target audience asks around ingredients, for instance "with which meals can I combine basil?" or "to which dishes does red pepper fit?"

Example 2:

Or assume, I would like to find out questions around fashion people are searching for, for example, "how to combine white jeans?"

So far, I have these ideas:

a)
I could use the autocomplete / suggestions function of Google. But when I (to stick to the example) enter the keywords "basil" or "white jeans" there, it displays not a single question, containing the given keyword.

b)
Do (ideally free) SEO tools exist that can find me question queries that contain keywords I provide?

Or maybe you have other approaches, how I could find corresponding question queries around keywords I provide?