SuStel:

chang'e' DaH Sam Find Chang now!
In this context, I believe the sentence
can be interpreted like so: Chang! Find him now!
That is, it's using the object noun as a topic instead of a focus.

SuStel:

The parallel sentence in TKD gives us what seems to be a focus interpretation
(HaqwI''e' DaH yISam Find the SURGEON now!), but no context is given, so it's
a little hard to interpret.

I'm afraid you lost me here; the {chang'e' DaH Sam} and {HaqwI''e' DaH
yISam} seem identical with the only difference being that the first
uses clipped klingon.

So, couldn't there be the opposite interpretation as well, i.e. the
{chang'e' DaH Sam} using the focus function of {-'e'}, and the
{HaqwI''e' DaH yISam} using the topic function {-'e'}?

Yes, that's why I said the various functions of -'e' are closely related, and I think pushing the object out in front of the adverbial where other non-subject, non-object nouns might go further blurs the lines.

I agree with JanSIy that Klingons pay more attention to the context in which -'e' is used more than in trying to understand arbitrary distinctions in its use. I think fronting an object with -'e' might be changing its context from "special object" to "what the whole sentence is about."

Wikipedia article on topic (but note that the word focus on that page is used in a slightly different way than what we're talking about here): https://en.wikipedia.org/wiki/Topic_and_comment

Wikipedia article on focus: https://en.wikipedia.org/wiki/Focus_(linguistics)

Look over the beginning of those two pages, then compare them to what TKD says about -'e' in various places. You'll see that the use of -'e' in copulas matches what is said about topic, while the use of -'e' in subjects and objects matches what is said about focus.

-'e' on a non-subject, non-object noun is not explicitly addressed in TKD, and we have only one clear example of it, the one from ST5, and it matches the description of topic, not focus. The examples in the TKD Addendum of moving the object to before the adverbial might be an example of this, but this is not made explicit or denied. When Gorkon shouts chang'e' DaH Sam, is he saying As for Chang, find him now! or is he saying Find Chang (not someone else) now! I'm not entirely sure, though I guess that it's the former. If that's the case, then it may be that "fronting" the object with -'e' is not just a syntactic trick, but means you're actually changing the context of the noun from being an object (where -'e' means focus) to being a non-subject, non-object noun, where -'e' apparently means topic.

But we don't KNOW any of this for sure, so I can't give you the solid answers you both keep asking for. Okrand himself admitted error in calling -'e' topic in TKD where he uses it as focus. I think he's not entirely clear on the distinction himself, or wasn't until Lawrence pointed it out to him. So, in general, try to use -'e' as focus when putting it on subjects or objects that aren't head nouns of relative clauses, and try to use it as topic when putting it on nouns at the end of copulas. For the weird cases, take your best guess.

-- 
SuStel
http://trimboli.name