Yes, POCOPHONE F1 support 4K video recording. Ultra High Definition or 4K possess 3840 x 2160 pixels, which are 4 times as many in Full HD or 1080p.
This massive increase in the number of pixels enables you to capture extra fine details with the following benefits:
You can find complete specifications here: POCOPHONE F1
Yes, Xioami Poco F1 supports VoLTE in both the SIM slots since VoLTE works on bands 3,5 and 40 and both the SIM slots in Xiaomi Poco F1 supports band 3 and 40. You can use two Jio SIMs at a time in Xiaomi Poco F1.
You can go to this link for complete specs: Xiaomi Poco F1