What is best practice to give priority to Skype users connected with wlan?
Keep in mind that Skype (for business) is tunneling VoIP over https. How would you give priority to these packages? Would you setup QoS to give priority by skype server IP and a script to look up skype connection dns and update ip as the dns changes? Or is there a better way to do this?

Topology:
Internet connection: 50mbit fiber
Router: RB1100AHx2
Accesspoints: 2x rb912

You can create an address list; for the IP ranges a simple Google will take you to Microsoft's list.
Then create a QOS scheme with a queue tree that will prioritize the traffic for you.
https://wiki.mikrotik.com/wiki/Manual:Queue#Queue_Tree

I was hoping the packets could be identified in some other way than by IP.

I work mostly with Cisco Jabber but I imagine it behaves similar. While the traffic is wrapped in TLS it is likely operating on a non-standard port for some of that data precisely so it can be identified. Looking at Microsoft's documentation that appears to be true. Particularly the audio, video and desktop sharing ranges. Which are probably the ones you care about the most.

That said you can set DSCP in a lot of ways. I tend to take the approach of trust but verify, in other words I check everything with an ACL to make sure it is marked appropriately. You can use Microsoft's own published address list and port number ranges to build a policy for the ports and IPs related to the actions you want to protect.

Just make sure to translate DSCP values appropriately between wired and wireless appropriately.

Microsoft's list: https://support.office.com/en-us/articl ... 2#bkmk_lyo
MikroTik WMM Wiki: https://wiki.mikrotik.com/wiki/Manual:WMM