The blueprint nodes are implemented in C++ so you can reference them to see how it is done. The “Get Binding” node is implemented in MovieSceneObjectBindingIDPicker.cpp, as FMovieSceneObjectBindingIDPicker.
You may also want to try looking at the source code for these sets of nodes, which are part of the Sequencer Scripting plugin.
FSequencerBindingProxy UMovieSceneSequenceExtensions::FindBindingByName(UMovieSceneSequence* Sequence, FString Name)
FMovieSceneObjectBindingID UMovieSceneSequenceExtensions::MakeBindingID(UMovieSceneSequence* MasterSequence, const FSequencerBindingProxy& InBinding, EMovieSceneObjectBindingSpace Space)