Translation:How much do you read on average on the weekend?
As I mentioned above, to me, "at the weekend" is not a phrase I would use (I've now lived in Canada for too long), but it makes sense to many people in Europe who consider the week to be Monday to Friday, inclusive (i.e., the business week) with Saturday and Sunday coming after/ at the end of the week or "at the weekend".
Preferred word order and preposition use varies from one English speaking region to another. Whereas Nic698651 prefers "at the weekend" that phrase would never, or almost never be used in Western Canada. There, the most used phrase is "on the weekend". And, the most usual word order results in the adverbial phrase being in first position so the English translation would read, "On average, how much do you read on a weekend?" but a more likely question is, "On average, how much do you read on weekends?" The use of "average" conditions the time frame and causes the singular noun phrase "a weekend" to feel strange to native speakers resulting in their use of "weekends'.