ETSManager API does not utilize the concept of the workspace in the same way as PTS GUI or PTSControl API do. There is no PTS workspace for ETSManager API.
At the same time, there is a directory where PTS stores logs and other files like link_key.txt or le_security_info.txt when the test cases are executed using ETSManager API.
The pchWorkspacePath parameter of InitEtsEx() API specifies the location where the files created during the automated test execution execution are stored.
To make sure that the files like link_key.txt or le_security_info.txt are properly created and discovered, set the working directory to the one specified in pchWorkspacePath right before executing the test case:
os.chdir("C:\Users\user_name\Documents\Profile Tuning Suite\<your_working_directory>")