Learn English – Is the phrase “Could I then…” correctly used in the following sentence

Person 2 is being dreadfully picky in my opinion. For one, to say that something "sounds very ghetto" as a negative is pretty insulting to anyone who lives in a ghetto. There are certain racial and social undercurrents to this statement that are far too complex to go into here as well. To get an idea for yourself, google "ghetto speech" and you will see a wide range of interesting material, as well as a good deal of hateful and racist commentary.

Suffice it to say that "where is it at?" as opposed to "where is it?" is somewhat "slangy" but also commonly used, at least in American English. Whether or not it is technically grammatically incorrect, it is common enough that most people just don't care.

Also, the informal idiom where it's at generally means a fashionable place where the most interesting things are happening at present. By extension, it can be used to refer to people, things or activities as well:

Studio 54 is where it's at.
Whole wheat spaghetti is where it's at.
Kant's Critique of Pure Reason is where it's at.

And so on.

In "most definitely", the word "most" acts as an intensifier to "definitely", which itself means "without any doubt; certainly". It has only one possible meaning.