水野史土

This plugin shows post/page/category/tag/comment/media/user IDs on admin’s edit post/page/category/tag/comment/media/user pages. You can see the ID when you visit an edit post/page/category/tag/comment/media/user page. 
Since this plugin hooks on ‘edit’ link, only users with priviledges can see IDs. For example, a user of author role can see post IDs, while a user of subscriber role cannot.
You can find a brief description in Japanese on a book <a href="https://php4wordpress.calculator.jp/" rel="nofollow ugc">Introduction to PHP for WordPress Users.</a> (written in Japanese.)

ShowID for Post/Page/Category/Tag/Comment

This plugin shows post/page/category/tag/comment/media/user IDs on admin's edit post/page/category/tag/comment/media/user pages.

erichie

Displays the Site Id (Blog Id) on the Network Sites page. This makes it easy to find the Site Id for each site in your Multisite install without looking in the database or editing code.

Multisite Blog Id's

Easily find the Site Id for Multisite blogs.

ShowID for Post/Page/Category/Tag/Comment vs Multisite Blog Id's