Depending on if there are caps, or where they are/how arranged, here we go on text exotes:
1.)
o.o : blank stare, as in "You've just lost me" Or "I care about this...Why, again?"
2.)
O.o ; o.O : Confusion, usually used together.
3.)
O.O : Suprise, shock.

From STEM, an abbreviation short for "Science, Technology, Engineering and Mathematics", a STEMlord is a pejorative term for a particular kind of person who has studied in these areas at university or works in these fields who holds a pretentious, condescending attitude to anyone who has studied in any other fields, particularly the Arts and Humanities. They typically believe themselves to be more "intelligent" and "rational", while generally remaining incredibly ignorant outside of their areas of expertise and having the charisma of a rotting pig's backside.

An anime style smiley used to express shock, or

shock, puzzlement, misunderstanding; raised eyebrow, skepticism

generally used in online chatting

A surprised, disturbed or confused emoticon.

it depends. either you use: o.o, O.O, O.o, or o.O there's a good chance it's for something you couldn't believe you just heard.

–emoticon

1. A commonly emoticon used on the internet to indicate confusion
2. A surprised look
3. (used to specify the feeling where you don't know what's going on)
4. Over-used in instant conversations like the internet short form of laugh out loud; "lol".

This emoticon has been used in several different ways. Some of them, you may recognize:

o.o , o.O , O.o , o_o , o_O , O_o , 0.o , o.0 , o_0 , 0_o , 0.0 , O_O , 0_0 , O.O

Aside from the ones given above, there have been several people who customized them. For example; o_______o , o_o;; , o_o" and so forth...