how can one tell that the first о in скорого is stressed?
By looking it up in a dictionary.
Russian word stress is, unfortunately, largely unpredictable: you can't tell just by looking at a word how it is stressed.
And sometimes, "the same word" can be stressed in multiple ways, e.g. окна can be either о́кна "of the window" (singular genitive, pronounced ókna) or окна́ "windows" (plural, pronounced akná), and замок can be either за́мок "castle" or замо́к "lock (to open with a key)".
I think you mean to say "that clears things up (for me)"? 'That clears me out' is like you're playing poker and you run out of cash, or someone robs you blind and you got cleared out. Not a very natural construction like this, but somewhat understandable in a different context. :)