It isn't a question of protocol (IMAP or POP) it is a question of whether the e-mail client, in your case the iPad e-mail app supports it, or if the e-mail service you are using (gmail) allows it.
There is no support on the iPad e-mail app for read-receipts.
Here is what Google says about gmail accounts and read-receipts:
Request or return a read receipt
To find out when people see an email message you send, request a read receipt. When the person opens your message, you'll get an email that shows the time and date of when it was opened.
Note: Request and return read receipts aren't supported in gmail.com accounts.
Request a read receipt
- On your computer, open Gmail and click Compose.
- In the To and Cc fields, enter recipients as you normally would, and write your subject and message.
Read receipts aren't returned for messages you send to a group mailing list or alias.
- Click More options
.
- Click Request read receipt.
- You won't see this option with your current account [email protected]. Read receipts are available only if you use Gmail with your work or school.
By "work or school' it means that you have a Google Account that was set up through your work or school, a club, or maybe family or friends. This is often called a G Suite account. If you also have
another Google Account that you set up just for yourself, you might notice some differences when using each account.
There are other ways though - see here
How to anonymously check if someone has read your email