There are 4 ways to pick the Jack.
For each of the 4 ways to pick the Jack, 
there are 4 ways to pick the Queen.
That's 4×4 or 16 ways to pick the Jack and the Queen.
For each of the 16 ways to pick the Jack and the Queen,
there are 4 ways to pick the King.
That's 16×4 or 64 ways to pick the Jack, Queen and King.

Here are all those 64 ways:

 1. J♥ Q♥ K♥
 2. J♥ Q♥ K♦
 3. J♥ Q♥ K♠
 4. J♥ Q♥ K♣
 5. J♥ Q♦ K♥
 6. J♥ Q♦ K♦
 7. J♥ Q♦ K♠
 8. J♥ Q♦ K♣
 9. J♥ Q♠ K♥
10. J♥ Q♠ K♦
11. J♥ Q♠ K♠
12. J♥ Q♠ K♣
13. J♥ Q♣ K♥
14. J♥ Q♣ K♦
15. J♥ Q♣ K♠
16. J♥ Q♣ K♣
17. J♦ Q♥ K♥
18. J♦ Q♥ K♦
19. J♦ Q♥ K♠
20. J♦ Q♥ K♣
21. J♦ Q♦ K♥
22. J♦ Q♦ K♦
23. J♦ Q♦ K♠
24. J♦ Q♦ K♣
25. J♦ Q♠ K♥
26. J♦ Q♠ K♦
27. J♦ Q♠ K♠
28. J♦ Q♠ K♣
29. J♦ Q♣ K♥
30. J♦ Q♣ K♦
31. J♦ Q♣ K♠
32. J♦ Q♣ K♣
33. J♠ Q♥ K♥
34. J♠ Q♥ K♦
35. J♠ Q♥ K♠
36. J♠ Q♥ K♣
37. J♠ Q♦ K♥
38. J♠ Q♦ K♦
39. J♠ Q♦ K♠
40. J♠ Q♦ K♣
41. J♠ Q♠ K♥
42. J♠ Q♠ K♦
43. J♠ Q♠ K♠
44. J♠ Q♠ K♣
45. J♠ Q♣ K♥
46. J♠ Q♣ K♦
47. J♠ Q♣ K♠
48. J♠ Q♣ K♣
49. J♣ Q♥ K♥
50. J♣ Q♥ K♦
51. J♣ Q♥ K♠
52. J♣ Q♥ K♣
53. J♣ Q♦ K♥
54. J♣ Q♦ K♦
55. J♣ Q♦ K♠
56. J♣ Q♦ K♣
57. J♣ Q♠ K♥
58. J♣ Q♠ K♦
59. J♣ Q♠ K♠
60. J♣ Q♠ K♣
61. J♣ Q♣ K♥
62. J♣ Q♣ K♦
63. J♣ Q♣ K♠
64. J♣ Q♣ K♣

Edwin