The free to air (non sky card) frequency for Channel 4 is 10714 H 22000 5/6.
This is the version that will be on the channel list on Freesat and Sky boxes.

There is a "stronger" alternative frequency for Channel 4, but it does require a Sky card, either a Freesatfromsky (FSFS) card or subsription card.
This stronger C4 frequency is 12480 V 27500 2/3, which you must add to your "other channels" list on your Sky box.

If you have a Sky card, and a Sky HD box , then you can use C4HD, on Sky channel 140.