Import .vob files in FcpX

HandBrake is another option.

VOB files have to be converted. I don't know if there is a better option, but VLC (https://www.videolan.org/) does a good job.

Open the app and go to Convert/Stream. You'll get a dialog where you can drag and drop the VOB file.

Choose a profile > click the Customize button. Select MP4/MOV in Encapsulation, Video Codec > H.264 (leave all the other values at 0 to have VLC use the highest quality), Audio Codec > MPEG4 Audio AAC or WAV; Bitrate 128 is ok, 2 Channels and Sample Rate 48000. Then Click Apply (Save as New Profile "For FCPX" if you're going to reuse this). Then select Save as File (set a destination). Then Go!

There may be other options, but VLC seems to do a good job of it.