In Office365/Graph Api you can view messages and events on the office.com Website via the weblink-property. However for contacts it seems to be missing or not implemented.
Is there any equivalent or workaround known for contacts, so a user could view/be redirected to the office.com (or any other Office365 page) webpage and view his contact there?
No, there is no similar URL property for Contact.
I'd suggest adding this to the Office Developer UserVoice. This will ensure it's on the Graph/Exchange team's radar.