cat aliasesedit

aliases shows information about currently configured aliases to indices including filter and routing infos.

% curl ''
alias  index filter routing.index
alias2 test1 *      -            -
alias4 test1 -      2            1,2
alias1 test1 -      -            -
alias3 test1 -      1            1

The output shows that alias has configured a filter, and specific routing configurations in alias3 and alias4.

If you only want to get information about a single alias, you can specify the alias in the URL, for example /_cat/aliases/alias1.