All the tokens that are available to your Drupal installation are listed on T...

All the tokens that are available to your Drupal installation are listed on Token's help page (admin/help/token). This includes tokens provided by Drupal itself, token module, and any other module that provides tokens.

Apart from this, many places show a link 'Browse available tokens' (or similar) to see what tokens can actually be used in that context. For example, field description on field settings page allows tokens but it may not be possible to use all possible tokens there. The link 'Browse available tokens' just below that will show which tokens may be used there.

I hope this helps.