Freezing a sour cream cake is not recommended because the sour cream when frozen changes texture and then will turn out like cottage cheese.
You can freeze the sour cream cake but the sour cream will usually curdle and change texture so the sour cream cake may not be as good to eat.
However the sour cream cake is still safe to eat when it's been frozen but it won't be as tasty.
I would recommend just refrigerating any leftover sour cream cake or if it's the whole sour cream cake just refrigerate it with some plastic covering and then eat the sour cream cake within a few days.
The longer the sour cream sits in the refrigerator the less tasty it becomes as it gets stale overtime and then eventually after around 5 to 7 days the sour cream in the sour cream cake spoils.