Can I subpoena my husband's bank account?

Yes.

Yes, but there are very strict rules to be followed and the bank will charge you for their time and the cost of copies.

Yes, but I recommend you use a local subpoena service to get the subpoena issued and served properly.

File a Request for Production of Documents asking for his bank account statements from all accounts in his name (or for which he is a signer) for a set period of time (ie, 12 months - 5 years).

In California, because you are representing yourself and don't have an attorney, you will need to have the court clerk sign your subpoena. This means you will need to prepare the subpoena yourself and need to specifically describe all documents that you want to have and the time periods that you are asking for them. Keep in mind, you will probably have to pay the bank for each page and a small fee for the time their employee spends researching and gathering the documents you request. You can also get the documents directly from your husband, by doing Discovery requests. The discovery process can be complicated, if at all possible, I recommend that you hire an attorney to make sure the requests are prepared correctly and you are getting the information you need.

If you are representing yourself, I'm sure its because you either can't afford an attorney or don't want to spend the money, I would suggest you contact Legal Aid for free guidance.