they usually post it on the top of their site or send you a code via email. If you don't have a yoox acct, sign up so your elligible, but they just had a round of sales/free shipping so dont expect any..
Yoox advertises their own promotions on their site. I've googled for Yoox coupons a bunch and they are all for a limited time and the site tells you of them at the top of the page. They just had a free shipping couple weeks ago.
I posted the pics of mine awhile back- they are a DDG release of slammer with a darron leg opening and some very intricate embroidery detailing. Sweet pair IMO, but be wary of the blue wash version that pops up on ebay now and then that is fake