If someone has two accounts and he is going to merge between them, will he get the reputation of both accounts?
As long as there has been no cross voting between the two accounts then the merged account's reputation should be the sum of the two accounts reputation - subject to the daily reputation cap.
For example, if account A earned 150 reputation on day 1 and account B earned 100 reputation on the same day then the combined reputation would be 200, not 250 (unless some of that reputation came from acceptances or bounties).
However, if account A earned 150 and account B only earned 20 then the merged account would earn 170 for that day.
If there's been some voting between the accounts then you won't get all the reputation.