I interpret donkbets with 2 lines based on experience... one is the villain has some sort of draw (monster or not) and wants to see a cheap turn. Another line that I have encountered is villain donkbetting middle pairs on low flops to get more information on his hand. If I have air Id raise most donkbets and keep barreling on dry runouts. If I have top pair for instance Id call and control the pot. 

We could consider raising turn as a semi-bluff.  River is extremely tough as played and I don't fault a call.

This really depends on the history of the guy donk betting to me. Is he someone who donk bets to entice a raise, get information, or see a cheap turn? If he is the last 2 out of 3 I'd most likely raise the flop and fire most turns if checked to. If you feel he's a more competent player and is trying to entice with the donk then just call as you did. On the turn as played I definitely semi bluff raise with the intentions of shutting down if he calls. If you just call and miss you're going to be calling a lot of rivers anyway so you're not going to lose much more than you would semi bluffing the turn. The river is meh, as played I'm probably folding, but again, with no mentioned reads on villain I can't really give an accurate suggestion. I just don't see people donk out and fire 3 streets with complete air too often, which is about all you beat.

It really depends on the villain's tendencies. Leading the flop can be an attack on your range (bluff, semi-bluff), or a value bet. Probably the most useful thing I was told was to consider leading stats and 3B stats together - if villain 3B's a reasonable amount, then how strong can his value bet leading be? If he hardly ever 3B's OOP then his leading range, particularly on this drawy board is usually for value.

I really like this line. We want to maintain our equity, and usually against donk bets if they have value hands I dont see too many people folding.  Once he fires the 3rd barrel, I dont expect him to have any bluffs in his range, especially when the board pairs.