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 Q<=Q; end endmodule