In a divorce can a husband use information from his wife’s diary?

There is no inherent legal bar against using the other spouse's diary. However, the diary might end up not being admissible. For example, it may be considered hearsay (the "words" of a person not made in court, under oath)--though there are ways around this (characterizing it as an admission against interest; using the diary to "impeach" contradictory testimony of the wife)--or under some circumstances, if the husband obtained it improperly, a court could deny admission to the diary on grounds it would be inequitable (or unfair). So the short answer is, while it's possible that the diary could  come into evidence, it should not be counted on--and if the diary is likely to be a critical piece of evidence, the husband should get an attorney to represent him, to help make sure it can be used (or the wife should get an attorney to maximize the chance of keeping it out of court).

That may depend on how you intend to use the information and your state laws on privacy.  Some states have held that the one whose diary it is holds a right to privacy of the information conained there in.  That can obviously be subject to the particular facts of the situation. Do you wish to use it to prove say adultery?  I would speak with an attorney in your area on the matter.  Good luck.