I already have a phisical copy of xanathars guide to everything can I scan it for a digital copy?

I think this user is asking if there's a way to scan a code and unlock it on D&D Beyond. The answer is no, you cannot. Most of the books do not have any sort of redeemable code with them, and the very few bundles that do have a code are clearly marked.

Please read here for more information: https://www.dndbeyond.com/forums/d-d-beyond-general/d-d-beyond-feedback/96069-hardcover-books-d-d-beyond-and-you-faq

Quote from Stormknight >>

Unfortunately, there is no possibility of backwards granting access to content on D&D Beyond, for free, based on physical books you already own.

On top of other reasons, there is no way to legitimately discern who has purchased a physical book (barcodes/receipts etc are not viable).

With regards future book purchases, we are exploring options. We're not able to share what that might look like as, at this point, it's still exploratory.

Whilst probably not the answer that you wanted to read, I hope this provides the answer requested.

Before WOTC purchase DND Beyond they were 2 separate companies. 

If you purchased a physical book and DNDB was to give you access they would be doing that at zero net profit. 

However, I do think going forward that WOTC will make both versions available.

the new Dragonlance book, if you pre-ordered it direct from WOTC you received a code as well. 

There were a few situations in the past where there was a code in the book, but not often. 

Quote from bobberuchi >>

 

There were a few situations in the past where there was a code in the book, but not often. 

Once, it has happened once before with a code in the Essentials Kit for the adventure for free and 50% off the PHB.