硕士毕业后申请了opt,博士毕业后还可以申请吗?
yes
第二个问题:
申请H-1,需要公证大学毕业证书吗?中国大学,美国硕士。
It depends on which degree is used for the H1 profession. If master's is in the same field for the position, master's is enough and bachelor's does not matter.
第三个问题:
考CPA,需要公证大学毕业证书吗?
This is none of US Immigration's business and you don't need USCIS's approval for this.