1.2v means that the power supply voltage for this memory id 1.2V. Additional requirement for the System Memory of this NUC you may find on page 15 of Product Specification https://www.intel.com/content/dam/support/us/en/documents/mini-pcs/nuc-kits/NUC8i7HNK_TechProdSpec.pdf . Usual Intel publicizes a list of Intel Verified compatible products (including tested RAM memory modules), however such list doesn't exists for this product yet.
In the following links you will find first reviews of NUC8i7HVK provide by Intel for test:
In both review the memory used (provided by Intel), was Kingston HX432S20IB2K2/16 https://www.kingston.com/dataSheets/HX432S20IB2K2_16.pdf . Yes, I saw it - this memory modules where tested by the manufacturer to run at 3200MHz, while the NUC8i7HVK calls for 2400MHz, however it works (and the memory speed is correctly detected in BIOS as 3200MHz) according to the test performed.
Hope this helps