Assume that whenever Villain donkbets you, that you are going to get called unless his donkbet is a minbet or something.
So with having that said, its pretty safe to calculate it from there so if he folds, well then you win it ofcourse

so
Pot + Your Stack that is going to call + your stack : Your remaining stack
$0.85 + $1.6 + $1.6 // $1.6
$4.05 / 1.6
2.5/1 = 28% you need.
But apart from that, I would fold this one because there are Two :ds, a King which makes your Jack rather useless and discount your Ace

which leaves you with 2 clean outs BUT even then, if you face AK, your actually drawing ''dead' more or less. For 2 outs you need 11:1 based on 2 cards to make it +EV
As you can see, its a clear fold.
- Gerv