Yes, LG V30 Plus does have the headphone jack.
Yes, LG V30 Plus can record 4K videos very easily as the rear camera has the highest video recording resolution of 3840 x 2160 pixels. You can also record 4K videos with Hi-Fi audio recording.
Yes, LG V30+ does have the OTG support.
Yes, LG V30 Plus does have the QUAD DAC which you can term as much superior to Dolby Atmos.