My bullmastiff dog has eat a sock what will happen to my dog will he pass it throu

There is really no answer to that. It may pass through without incident or it may become lodged or tangled.

Just keep a close eye on him and watch out for any signs of distress.
Things to watch out for include:
Lethargy
Vomiting
Constipation (trying to 'go' but can't)
Blood in the stool
Tightening of the stomach

You know your dog best, so if you see any behavior that is out of the norm it would be best to have him seen to by a vet as soon as possible.

Not trying to make you panic, mine have eaten all sorts of things over the years without incident but there is always a chance something could go wrong.