Get all the fields attached to an term
You can use field_info_instances() which:


  Retrieves information about field instances.


In the case of taxonomy terms the code would look like this:

$instances = field_info_instances('taxonomy_term', $vocab_machine_name);


The $instances array will contain (amongst other things) the machine names of all the fields attached to the term, if you want further information about any or all of those fields you can run the names through field_info_field().

I think the file that function lives in is included by default but if not just add this before you call it:

module_load_include('inc', 'field', 'field.info');