The Mac has had, as a standard feature for decades, an on-screen keyboard to allow you to explore the results of different key combinations. It’s a great tool.
I should note that, alongside it, is a useful search tool that allows you to find the character you’re looking for if you’d rather just search and don’t care to learn the key combination (if there is one).
In Mojave, and it’s pretty similar across versions IIRC: open keyboard preferences in system settings and check the “Show keyboard and emoji viewers in menu bar” box.
That will replace the language flag icon in your top bar with an odd icon with the command key embedded.
The second option in that menu is the keyboard viewer. You can show that and drag on a corner to make it as large as you want. Dynamically changes the keyboard as you hold down modifier keys.