I want to buy a domain the contain the word "Logitech" and model number . com How can i know if they allowed to buy this domain??
Bad idea without getting prior permission. Sometimes in certain industries the company will allow it but it's highly unlikely Logitech will be happy with that once they found out. A better idea would be to register a broader domain, create a Logitech category and branch off subpages with their products and so on.
you need to do a trademark search before you buy a domain name,If you don't, You Take the Risks, It's a big risk.