In the Knowledge Base we use the default standard names of the issue field.

But in many cases, you will have renamed the fields to suit your purposes better.

Sometimes you still need to know what standard field your issue field corresponds to.

You'll find this in the issue(/task/ticket/etc..) field configuration page. (The actual name depends on your chosen terminology. But here we go with issue field configuration.)

1. Go to General - Settings - Issue configuration - Issue fields. 
2. Select the issue field configuration that is used in the relevant project and open it
3. Go to the row that corresponds to the issue field that you need to examine
4. Click on the green or blue "?"-icon to open the issue field information.

This dialog shows the standard name of the issue field in English, or notes that it is a custom field.

Quick tip: Issue fields with green icons are standard fields, while custom issue fields have blue icons.