If I get a new iPad online will the Apple store sync it up with my trade in ipad

Whilst the technicians at the Genius Bar of your Apple Store can help with setup of your new iPad - and transfer of data from old to new - it really is a straightforward process.

These support pages should get you started with setup of your new iPad - and the methods of transferring your data from old to new iPad:

Set up your iPhone, iPad or iPod touch – Apple Support

Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support

Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support

If the donor iPad, from which you are transferring your data precedes iOS12.4, QuickStart will not be available.

“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the new device. Nothing is moved or removed from the original device.

An alternative is to restore either an iCloud or iTunes backup to the new device:

How to back up your iPhone, iPad and iPod touch – Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

My compliments to Lotus for providing a much more complete answer.

I’d only add to NOT overlook the “housekeeping” tasks required w/ you “old” iPad.

Remember, that is YOUR - very identifiable - data. Make sure that YOU thoroughly “sanitize” it prior to final transfer to anyone.

https://support.apple.com/en-us/HT201351

Here are the steps involved:

https://support.apple.com/en-us/HT201269

It’s a straightforward process you can perform yourself, but any Apple Store would be happy to help you thru it.