I had gout attack on my right foot about a week ago and the doctor prescribed me prednisone 4mg and the gout was gone a way. two day ago, the gout was pop up on my right knee. how long can i take colchicine 0.6 mg and allopurinol 100mg together?

With that history, I strongly suspect your kidney function is not perfect because you were prescribed steroid for acute gout, not colchicine. I said that because you are taking only 100 mg of allopurinol, a usually adjusted dose for patient with CKD. Even with CKD, you can take both colchicine & allopurinol, with adjusted doses & caution. Without CKD, you are fine to take both as long as needed.