"Can everybody hear me? Am I speaking up enough?" "Can everybody hear me? Am I loud enough?" Both are correct and would be understood. You might hear the second one more often.

"Can everybody hear me? Would you like me to speak up?"

Go to the back of the class. And ask the question.

sorry I did not pay attention to the question. I was thinking how to make sure you can be heard.

Know your room. I always make sure everyone can hear me before I begin.