The mistakes in the sentences are as follows:

1. In sentence 1: "go always" should be "always go." The correct phrase should be "Does Nam's mother always go to work by bus?"

2. In sentence 2: "will want" should be "want." The correct phrase should be "You have to work hard if you want to pass the exam."

3. In sentence 3: "on July" should be "in July." The correct phrase should be "He always visits his grandparents in July in Yen Thanh."

4. In sentence 4: "go" should be "to go." The correct phrase should be "I wish that I could go to class earlier."

5. In sentence 5: "knows" should be "knew." The correct phrase should be "He wished he knew the answer, but he really doesn't know."

6. In sentence 6: "enough deep" should be "deep enough." The correct phrase should be "parts of the oceans that are deep enough for people to explore safely."

Therefore, the mistakes identified for each sentence are:

1. **A:** Error: "go always" should be "always go."
2. **B:** Error: "will want" should simply be "want."
3. **C:** Error: "on July" should be "in July."
4. **D:** Error: "go" should be "to go."
5. **A:** Error: "knows" should be "knew."
6. **B:** Error: "enough deep" should be "deep enough."

Each sentence has its specific mistake. Let me know if you need more clarification on any specific sentence!