Destroy it, then pick it up.
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Unfortunately you can't pick up cake when it has been placed.
Use a bucket
Mine it using a pickaxe (wood or better), then pick up the drop.
you need a mod. example: with the more creatures mod you can pick up rats, mice, and tamed cats.
If you are looking for a way to pick them up, well, you can't pick mob spawners up. You can only destroy them with a pick but it can give you a lot of exp.