1. The Asus Z170-A motherboard is on the G.SKILL F4-3000C15D-8GVRB QVL list, so your Z170-K model should be close enough.
2. Yes, the 2 ram sticks are compatible. Make sure the ram is located in slots "DIMM_A2" and "DIMM_A4".
3. 2133MHz is the fastest speed your motherboard will run memory without overclocking, so don't bother to Enable XMP, just set your memory speed, voltage and timings manually in the UEFI bios.
https://www.gskill.com/en/product/f4-3000c15d-8gvrb
The Asus Z170-K motherboard manual: 1-8
• The default memory operation frequency is dependent on its Serial Presence Detect
(SPD), which is the standard way of accessing information from a memory module.
Under the default state, some memory modules for overclocking may operate at a
lower frequency than the vendor-marked value. To operate at the vendor-marked
or at a higher frequency, refer to section 2.5 Ai Tweaker menu for manual memory
frequency adjustment.