Fun fact: ALE doesn't check your code. ALE doesn't produce any warnings.  
What ALE does do, it *runs code checkers* that do the actual code checking and aggregates their output.

The question doesn't say but it's pretty obvious this one's about Python.

Now, if you just call `:ALEInfo` (the single command you need to memorize when using ALE), you will see which tools are run and the warnings they report. It's a lot of text and you will need to scroll down a while.

In my example, I see
 
    C0103 (invalid-name) Function name "camelCase" doesn't conform to snake_case naming style

reported by `pylint`.

Now you can Google how to shut `pylint` up.  
I'll show you two ways. You can set a variable for ALE to forward to `pylint`

    :let g:ale_python_pylint_options='--disable=C0103'

or create a simple `pylintrc` like this one

```ini
[SECTION MANDATORY BUT IGNORED]

disable=C0103
```
And the warning is gone.

BTW, [PEP-8 wants snake_case](https://peps.python.org/pep-0008/#function-and-variable-names) so it would be better to just use it instead of disabling the warning.