Most of the major payers all have provider newsletters they send out regularly with any coding or reimbursement policy updates. The archives to these are typically housed on the insurer's websites as well.
You should be able to find the answer on each payer's website, whether in the newsletter or a policy bulletin. (Side note: I only trust the official source for insurer policy information. There may be sites that claim to have comprehensive lists, but how do you know it is the most current information unless you verify directly for yourself on the insurer's website?) If you're expected to research information for your employer, you'll want to get comfortable navigating the applicable payer's websites to find information. It will become more comfortable the more you do it.
As an example, here's a link to the United Healthcare website for providers:
https://www.uhcprovider.com/
On that UHC website under the resources menu, you can navigate to the Administrative Guides and Manuals, Education and Training, News (that's the UHC provider newsletter & archives), etc.
Additionally, there's a search box at the top of the page - if you're looking specifically for information about one particular code, you can pop that code in the Search box and get whatever results on that code are available on the website.
For example, when I put G2211 in the search box, one of the first suggested results is UHC Commercial's
Add-on Codes Policy, Professional https://www.uhcprovider.com/content...mm-reimbursement/COMM-Add-On-Codes-Policy.pdf
You can scroll through that document to see how UHC reimburses add-on code. There's also an attachment hyperlinked within that policy:
Add-on to Primary Code Relationship List - This table includes Add-on codes which will only be reimbursed when reported with the appropriate primary code. https://www.uhcprovider.com/content...dd-on-to-Primary-Code-Rltnshp-Policy-List.pdf
G2211 is listed on that attachment with the primary codes that UHC expects it to be billed with, under the conditions specified in that Add-On Codes Policy.
Each payer's website is set up a little differently, but most do have a lot of information for review. The search box is definitely your friend on those sites!
Good luck.