How do you plan to solve it?
module jk_ff_enable ( input CLK, input EN, input J, input K, output reg Q ); always @(posedge CLK) begin if(EN) begin case({J,K}) 2'b00 : Q=Q; 2'b01 :Q=0; 2'b10 :Q=1; 2'b11 :Q=~Q; endcase end else begin Q=Q; end end endmodule