If a “tittle” sits atop an “i” or a “j” (“ı” or “ȷ”), then where do “jots” sit?

Solution 1:

Jot and tittle are both technological waste; scraps on the floor, left over from a few millennia of literacy technology. There isn't really a meaning distinction between them; both are nonce forms that refer to any small chunk of writing.

And both are used mostly as NPIs in negative contexts, especially in the open Verb + Minimal Direct Object Construction, e.g drink a drop, do a thing, give a damn/shit, lift a finger, bat an eye, eat a bite, ...

Jot comes from the Hebrew letter Yod (י), the smallest letter in the alphabet, representing /i/ and /y/ (to the extent they are different in any given language). When Greek adopted the Semitic alphabet, Yod got renamed Iota, and iota is also used in negative contexts:

• He hasn't done one jot/bit/scintilla/iota of work.

Tittle is a variant of title, a word borrowed from Latin, where the sense of 'little bitty piece' of writing was fixed in Latin usage, according to the OED. It appears almost exclusively in the fixed phrase jot(s) and tittle(s).

In English, some have apparently reanalyzed jot as representing the dot on lowercase I, but that's just because it's the smallest chunk of our writing system. That dot on the lowercase I and J is just another example of a diacritic mark, like ö ő å í è ç š ū ñ.

Turkish uses both dotted i /i/ and undotted ı /ɨ/ to represent different (but related) vowels. İnterestingly, their respective capital letters are also different -- there's a dot on one (İ, i) but not the other (I, ı).

Solution 2:

http://oxforddictionaries.com/definition/english/jot

jot
noun
  a very small amount:

Origin:
late 15th century (as a noun): via Latin from Greek iōta, the smallest letter of the Greek alphabet

The Greek letter iota doesn't have a tittle, so every jot and tittle refers to the ı part and the dot on top.

The answer to the question is "On the baseline".