Joomla Template Manager provides an easy way to reveal the available module positions of the active template on each page.
First you have to enable the feature from the backend.
From the Admin Menu, Go to:
- Extensions -> Template Manager.
- Click the Options Button, on the Toolbar.
- In Template Manager Options, enable the Preview Module Positions (if disabled).
- Save the options.
With the feature enabled, you can now force Joomla to preview the module positions on each page in the front-end, you want to see the them.
Do with the following:
Add at the end of the url the "tp=1" parameter/value.
- With SEF URLs enabled, add "?tp=1", at the end of your sef url.
- With SEF disabled, add "&tp=1", at the end of the url.
- Click enter to re-load the page with the new parameter.
Joomla will display the available module positions of this page.
Thanks to Lodder's feedback below, I should mention that is a good practice to disable this feature after finishing with the task of viewing the module positions.