Reconize JK Flip-Flop operating edge: rising or falling?
The heart of the circuit is the pair of 2-input NAND gates which form a latch. Such a latch is active-low on input. This means that it will be activated when one or both of the 3-input NAND gate outputs goes low. This will happen when all inputs are high.

So the circuit is activated on the rising edge. When it does so, the latch is driven high or low, and the inverted feedback then disables the input.