George,
Do you mean where does the Data Domain Service fit in the TBM Model? I'm assuming you're asking where you would find/place the cost of someone that is in data architecture/data domain? If so, those are technical services that usually fall in architecture (ITRT) and roll up to architecture (services). The model is flexible in that you can add additional sub-towers or service levels to capture the type of function you're talking about. Hope I'm looking at this correctly.
If you're talking about Data Management in TBM. Then it's part of the TBM process.
1. Identify Financial Data
2. Identify Operational/Business (Infra, Projects, Apps, Services, and etc) data that adds color to the financials.
3. Transform and Model Financial and Non-Financial Data to allocate Financial costs to the different IT domains.