For an update on the situation, I did ask the question directly of Service-Now, and they said there is currently no functionality available (on our end or theirs) to discover this sort of detail. They have opened an enhancement request on my behalf.

Tony, I completely agree with you that protection from certain technical details is a major benefit of the SaaS model. My challenge is that we may be implementing an enterprise content solution that includes the ability to search Service-Now data, and the size of the index that this new solution creates will depend on the size of the data it is indexing. In order to calculate storage requirements, etc. for the new solution, it would be helpful to know how much data it will be working with.