Trying to export xyz data from TIN nodes (or STM) into a txt file - what's the procedure?
The best option would be to import the TIN/STM as a mesh then drop elements until you just have line elements.
After that you can use the extract points tool to extract the desired node points. You will have to do some cleanup on the file using the data cleanup utility.
Once you have just the points in the file you can use the export coordinates tool export to a txt file.
You may want to refer to the following:
https://communities.bentley.com/products/microstation/f/z_-archived-microstation-v8i-forum/76675/wanting-to-extract-points-from-a-mesh
https://docs.bentley.com/LiveContent/web/MicroStation%20Help-v15/en/XYZTextExportCoordinates2.html