How do I know if someone left a talk on a page?
- Click preferences at the top of the page. Scroll down.
- Register your email. You'll need to verify if you haven't already.
- Select your notifications, including E-mail me when a page on my watchlist is changed.
- Watch the page (using the tab at the top).
This will give you notifications for any change to the page or it's talk page. You'll only get an email the first time it's changed, unless you visit the page. If you visit the page, you'll get notified of the next change after that; if you don't, you'll get no more alerts.
Is there a Talk page for the all pages?
Yes, every page on a MediaWiki wiki has this. The tab is marked "Discussion" at the top, towards the left. Also, Recent Changes (on the left sidebar) is a great way to track everything that's happening on the wiki. It will show any and all changes made.