1. I have seen many sentsences where the dependent clauses don't have subjects like this. Would you say this is a correct sentence?

If composed as follows, it will be great.

If dealt as such, it would generate a different result.

2. Should the underlined parts with the hypen or without?

They are adult-centered. OR They are adult centered.

They are listener-based. OR They are listner based.

3. What do you call the kind of noun like the underlined/illustrated noun?

Professor-researchers are welcome.
1.The sentences have elliptical structure.They do not have an agent either. Some verbs are so commonly used in the passive, without mentioning an agent, that they work in a similar way to -ed adjectives.

2. 'Listener-based' is a compound expression: it needs a hyphen.

3. Compound noun (no hyphen here, not compound-noun but compound noun)
'Professor-researchers' refers to a title: it is to be hyphenated.
Thank you.

As to No. 1, I posted previously with the following two sentences and asked whether these are fine grammatically.

I think the answer or response to that post was this: You need some kind of an object.

The sentences I posted were/are???:

Please let me know if getting better.

Please let me know if done right.

Don't they have the elliptical structure that are workable??? in terms of their writing style or sentential structure ?

Sorry, this just came up. Should the underlined and colored part be were or are?

As to No.2, I think a post in this forum had this reply to the issue of whether the "noun plus participle" structure require the hyphen: The hyphen is not necessary. Please look at the thread titled "Noun + participle always with hyphen?".