Recently my friend saw what I wrote as reviews on every application I downloaded. Is it possible to see another friend's reviews & ratings? How?
When looking at reviews in iTunes for iOS apps, you can click on the username of the reviewer, which will bring up the reviewer's page and will show all the reviews that the user has left on apps. This does not work with the Mac App Store.
This is a random user's reviews I found by opening the reviews on the F1 2016 app. Clicking the username takes you to this page.
If you want to see all your own reviews instead of another user's, see Is there a single place I can see all the app reviews I've written in the iOS App Store?.