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.

KLicheR

Create a unique ID to easily identify repeater field’s rows. The field is fulfill on the first “save” of the post.
Compatibility
This ACF field type is compatible with:
<ul>
<li>ACF 5</li>
</ul>

Advanced Custom Fields: Unique ID Field

Create a unique ID to easily identify repeater field's rows.

ShowID for Post/Page/Category/Tag/Comment vs Advanced Custom Fields: Unique ID Field