1)Would the boy be facing down or up as the dragon eat him?
Probably face up.
2) How long would it have taken the dragon to have swallowed down to the boys waist ?
Given that you wanted him eaten like the dragon ate the pig, only a few minutes.
3) I would imagine that the dragon would pause for a moment to catch it`s breath once it had swallowed the boys upper body ,what would it`s tongue be doing at that point ,what it be licking at?
Actually, because its mouth would still be stuffed with the boy's body, it probably would just have its tongue still under the buttocks.
4) As you said the dragon would not really notice the boys swim trunks , how would it be able to tell that what was inside the front of the swim trunks was more tender and less bony and more meaty?
Because it will give more in his mouth than did the upper body with the skull, ribs, etc....
5)depending on how the boy is laying what part of the dragons mouth would come into contact with the very large looking buldge in the trunks ?
The upper part of the dragon's mouth.
6)How long would it take the dragon to eat the area in the trunks ,and given that the boy is not dead but knocked out ,could he possible feel it eating it ?
Even if the boy woke up at some point, by the time the dragon got to this part, the boy would be in shock.
7) once it had finished eating the boy hole ,and wandered off to rest /sleep while it digested the meal,were would digestion start first.would the boys small blue swim trunks hinder /slow down the digestion of the ample size flesh in them ?
No, the digestive juices would soak through and the flesh would be quickly digested.
8) From the info you give , the Dragon will digest all of what it can of the boy in about a day ,will the swim trunks still be hole given that they had been swallowe intact , will the other boy and his father and brothers be able to pick them out of the pile of vomitus ?
Yes, they would be whole and recognizable. They would probably be faded.