The ISPFListDocRevSnapshot interface exposes the following property:
SPFSnapshotDataGraphDef - The graph definition UID of the graph definition to use to get the data for the snapshot data file.
In the out-of-the-box configuration, we deliver a default graph definition that is used to get the data for the snapshot data file (DGD_SPFLLALineListRecordDocumentRevision). This graph definition is related to the ISPFLLALinelistRecordDocumentRevision. During the creation of the line list record document, the UID for this graph definition is written to the SPFSnapshotDataGraphDef property.
You may also wish to review the topic ISPFLLALineListRecordDocumentRevisionSnapshot.