In the TRKD API Developer's Guide, it mentions that "all TRKD API service operations are aggregated into throttle groups. A throttle group is a combination of TRKD API service operations that are throttled as a single entity". Where can I find the groupings of all the throttle groups?
Generally, operations are grouped by service ... so the throttle limit for your account applies to all and any operation in the one service.
In some case, notably Quotes related services, then the grouping is across all operations and services that hit the same backend ... for example Quotes, Quote Lists, Quote Chain and Portfolio Tracker all belong to same throttle group and thus the throttle limit applies to any operations in any of those services.