neither in the telescope description in the build menu nor in the tooltip for the telescope itself does it say it needs oxygen. I had to look on the forums to figure out why my duplicants wouldn't use the telescope since they were in atmo-suits and it wasn't ever mentioned that they needed oxygen to use the telescope. This requirements should be mentioned in those tooltips.
Steps to Reproduce
Look at the telescope tooltip in the build menu and look at the telescope when clicking on one built in the world.
This issue has not been confirmed by a developer yet.