Not much juice in options (puts or calls) in this ETF. My view is you enjoy the return and put in a stop order at 35. If it falls it could go quickly in any sign of inflation or weakness in this quality bonds. The bonds in this ETF are by and large medium grade compared to some.
Most "junk" bonds are illiquid in the sense that there is normally a big spread between the bid and asked. Many of these bonds don't even trade every day. JNK is a way of holding less than investment grade bonds and still being able to trade without concern for a bid/asked spread.
JNK is also an opportunity to buy junk that is professionally managed in the sense that they don't have to own all of the securities that make up the index. Since it is pretty clear that Moodys, Fitch and S&P ratings are less than reliable, it is likely that any purchase under NAV is a good buy.