The templates command provides information about existing templates.

% curl 'localhost:9200/_cat/templates?v=true'
name       template order version
template0 te*      0
template1 tea*     1
template2 teak*    2     7

The output shows that there are three existing templates, with template_2 having a version value.

The endpoint also supports giving a template name or pattern in the url to filter the results, for example /_cat/templates/template* or /_cat/templates/template0.