Why this sentence doesn't require a conjunction or a semicolon?

[Victor]

The sentence: Can you tell me why I am so obsessed with you?

I wonder why this sentence does not require a conjunction or a semi-colon for being a valid sentence. As I know, a valid clause means that there are only one subject and one predicate (I actually see it as a verb instead, as a predicate must contain one). Now, I am seeing this sentence as two parts, two independent clauses:
1) Can you tell me why?
2) I am so obsessed with you.

Unless the word "why" could act as a conjunction, I really do not understand.

Recently, I am reinforcing the infrastructure of my English, so if my questions unfortunately seem too naive to you, please kindly pardon me, thanks and sorry.

By raising this query, I have encountered another doubt again... I wonder if it is valid to have two conjunctions to connect two independent clauses?
For instance:
Unless you forgive me, otherwise I am going to be very upset.

Thank you very much.

[Marius Hancu]

The original sentence is correct.
See the equivalent:

Can you tell me the reason for which I am so obsessed with you?

[Marius Hancu]

>Unless you forgive me, otherwise I am going to be very upset.

This is wrong. Try:

Unless you forgive me, I am going to be very upset.

Take
unless: except if

[OddThomas]

Also, look at your sentence this way:Can you tell me [something]?
Something is the direct object of tell. And what is something?something = why I am so obsessed with you
Putting the parts together produces:Can you tell me why I am so obsessed with you?

[Eddie88]

To add onto OT's point, the direct object is in the form of a noun clause.

Search this on google, and this may help to clear things up

[Eddie88]

Unless you forgive me, otherwise I am going to be very upset.

Unless is a subordinator beginning a dependent clause (adverbial).

Otherwise is a conjunctive adverb--a word that cannot join two clauses by a comma--and a word that cannot join a dependent and main clause.

I will forgive you; otherwise, we will remain single.

I will forgive you. Otherwise, we will remain single.

If you don't forgive me, otherwisewe will remain single.

[Victor]

Thanks for everybody's helping hand. I have learnt a lot in this post. :)