xdiagnose can be quite a useful tool for some issues concerning graphics cards, although not particularly for suspend/resume issues as they are to do with the ACPI implementation of your laptop. There isn't a manpage for
xdiagnose and the
--help option relays a pretty terse selection of commands. However, the utility is really used for diagnosing and repairing Xorg issues, even though it could be the case that the Xorg server might be locking up on resume.
You can use
xdiagnose -v & to track X errors in a general way and let it run in the background, and the 'extra graphics..' option in the pop-up screen (see screenshot) can be ticked to send more graphics debug messages to
dmesg. Even though this information doesn't concern suspend/resume directly, the results might indirectly be useful if X is freezing on suspend or resume.
You can get information regarding ACPI by using grep to search
/var/log/pm-suspend.log for ACPI, suspend, and hibernate errors.
There are also a lot of references to Dell Latitude laptops on Ubuntuforums, so there should be some useful information there; but to answer your specific question,
xdiagnose isn't really that useful for diagnosing suspend/resume issues. See this Ubuntu wiki page and this one for a very useful and general account of how to debug resume/suspend problems.