M/S JK flip-flop response
A J-K flip flop is like a D type flip-flop except D is now a J and a K input, forming a AND gate of sorts.

In your image /Q and Q stop changing states if either J or K is low, or logic '0'. In this case J and K are low, so the toggle action stopped.

Note that a D type flip-flop will not self toggle unless /Q is wired back to the D input. A JK flip-flop already has this feedback loop in place, but both J and K must be logic high or '1' to toggle.

Also note that either type of flip-flop will change states only on the rising edge of clock, along with J-K both '1'. A D type flip-flop is actually a latch and would pass the value at D on the rising edge of clock. It will not toggle unless /Q is wired back to D.

You should have a state-chart that makes the JK flip-flop behavior more clear.