Let’s look at the difference between the number of sweets left. He had 14 more sweets left if he had given 2 less sweets to each friend.

Sweets remaining = 35 - 21 = 14
Number of friends = 14 ÷ 2 = 7
Number of sweets Daniel has:

Each friend → 8 sweets
7 friends → 7 x 8 = 56 sweets
Total sweets → 56 + 21 sweets remaining = 77 sweets

You can check your answer:
Each friend → 6 sweets
7 friends → 7 x 6 = 42
Total → 42 + 35 = 77 sweets