You can use a text filter on your column with this expression (dont forget to check the box 'regular expression' after you have copy-pasted this formula]
It means : find everything that it's not a unicode letter or a hyphen.
You can also play with fact -> Customized facets -> Unicode char-code facet.
According to the Documentation, "that generates a distribution of which unicode characters are used in a particular column. That distribution will allow you to spot outliers, meaning characters that are used infrequently and that might suggest encoding issues. You can use that char distribution facet to 'scan' and inspect the values for yourself and then use fix their encoding with the 'reinterpret' GREL function."
Hope this helps.