"Yes, I drink milk."
Translation:Ano, já mléko piju.
With your sentence you are stressing that you drink milk and not water or lemonade.
With "Ano, já mléko piju." you are stressing that you do indeed drink milk (and not the opposite).
I'm also trying to understand the subtleties of word order. I'm wondering if one could generalize that if the object follows the verb, one would translate it into English using the present progressive, as in ja piju mleko = I am drinking milk (now) vs. ja mleko piju = I (habitually) drink milk (eg. because it is a source of calcium, or in contrast to my vegan daughter who doesn't drink milk.) Am I getting close?
But... Well... This whole "word at the end of the sentence indicates it's stressed" is a hard concept to get your head around. Why would "piju" be more stressed than "mleko"? What else do you do with "mleko"? I guess there ARE some who take a bath in it, but otherwise...
Yes, it can even be an answer to somebody who bathes in milk. You say "Já mléko piju." to say that you drink it instead.
But normally "Já mléko piju." is used to say that you do drink. Perhaps someone else said he does not drink milk and you say that you do drink it as a reply.