I know I've committed to sites where I haven't fulfilled my commitment. Those commitments are no longer active; I've failed them.
How and where can I see what these commitments were?
You can't see your failed commitments anywhere as far as I know. You would have to go back to the individual sites and see yourself in the commitment list, and then compare this with your "Fulfilled Commitment" list to see which ones were failed.
You can go to your profile page. It will list the proposals that you follow. There are also two helpful sections:
Fulfilled Commitments
Commitments that you have fulfilled.
Current Commitments
These are commitments that are still pending. You can commit to three proposals at a time. Proposals with a green box are still in the commitment phase, and blue box proposals are in beta. All these commitments are unfulfilled.