Solution
The property SequenceFile.Path returns the path name TestStand used when the sequence file was last saved or loaded. In other words, you can get the directory path of the current sequence file by parsing the string value read from this property. Below is the required expression to do so:
Left(RunState.SequenceFile.Path, Find(RunState.SequenceFile.Path, "\\", 0, False, True))
For example, if the property SequenceFile.Path has a string value: "C:\Users\PC-Test\Documents\Sequence 1.seq"
The expression will return the following string: "C:\Users\PC-Test\Documents"