Risks are not identified prospectively, i.e. this is a case of “Fighting the Last Battle” syndrome, whereby management focus most on risks that have occurred recently.
Consider the last part of the sentence by itself. How would you phrase it if it wasn't part of a larger sentence?
Management focus(es) most on risks that have occurred recently.
What's the subject of the sentence? Management. The subject is third person singular (edit not exclusively. See the edit I added at the bottom of the answer), which means that it's grammatically equivalent to "he". If we can find the right answer for "he", then we know that that will also be the right answer for "management".
He focus(es) most on risks that have occurred recently.
Now, it should become clear to you that "he focuses" is correct, and "he focus" is not.
Knowing this, you can now correct your sentence:
Risks are not identified prospectively, i.e. this is a case of “Fighting the Last Battle” syndrome, whereby management focuses most on risks that have occurred recently.
Edit
Following an existing answer, "management" can correctly be considered plural by the COED:
[treated as singular or plural] the people managing a company or organization, regarded collectively:
management were extremely cooperative
That would mean that both singular and plural are correct, and you can therefore choose whether you use "focus" or "focuses".
"focuses" sounds better to my ears, but I accept that that may be a subjective judgment on my part.