1. You don’t can go to the party. => You can't go to the party.

2. He musts take his dog for a walk. => He must take his dog for a walk.

3. I can to help you. => I can   help you.

4. He not must be late. => He musn't be late.

5. Can his brother speaks French? => Can his brother speak   French?

6. Paul must to go there. => Paul must   go there.

7. You don’t must smoke here. => You musn't smoke here.

Ответ:

1. You can go to the party. [can - can't; перед модальными глаголами не ставится вспомогательный глагол]

2. He must take his dog for a walk. [В конце модальных глаголов s не ставится, даже с местоимением 3-го лица]

3. I can help you. [После модальных глаголов глагол ставится без частицы to]

4. He mustn't be late. [must - mustn't]

5. Can his brother speak French? [В вопросительном предложении с модальным глаголом ставится основной глагол без s в конце]

6. Paul must go there. [После модальных глаголов глагол ставится без частицы to]

7. You mustn't smoke here. [must - mustn't; перед модальными глаголами не ставится вспомогательный глагол]