I am not divorced yet, but can my separated wife touch any money in a joint broker account I have with my fiance?

Not unless it contains funds you had before date of separation. It is subject to discovery efforts by her lawyer.

Wisconsin is a marital property state. This means that while you are married all of your income, assets and liabilities during the marriage is considered marital property and there for it is 50/50 in nature with each spouse owning a 50% interest. This applies to all income, assets and liabilities that she has generated during the marriage as well. One way to legally avoid this situation is if you and your wife have a signed agreement whereby you each designate which properties or assets, incomes, and liabilities are exclusively your own. If you and your wife do not have such an agreement then anything you own with your fiancé has a marital property component and your wife has a claim.

Not if she is not on the account. However, she may be entitled to some of the funds in the account if you funded it with community property.

If it was earned during the marriage its probably owned by you and your wife. Until its awarded to you its subject to a restraining order.

Speak with your attorney, there are insufficient facts to answer. If it was you money and out of your income there will be a real issue depending on the circumstances. Get an attorney.