Get the (last part of) current directory name in C#

You could try:

var path = @"/Users/smcho/filegen_from_directory/AIRPassthrough/";
var dirName = new DirectoryInfo(path).Name;

You're looking for Path.GetFileName.
Note that this won't work if the path ends in a \.

This is a slightly different answer, depending on what you have. If you have a list of files and need to get the name of the last directory that the file is in you can do this:

string path = "/attachments/1828_clientid/2938_parentid/somefiles.docx";
string result = new DirectoryInfo(path).Parent.Name;

This will return "2938_parentid"