how do i know if a motherboard has built in wifi?

Solution
As an example, look here: https://www.asus.com/Motherboards/ROG-STRIX-Z370-E-GAMING/specifications/
You are looking for this part of specification:
Wireless Data Network
Wi-Fi 802.11 a/b/g/n/ac
Supports dual band frequency 2.4/5 GHz
Supports MU-MIMO

A board without wifi will not have such section in its specification.
As an example, look here: https://www.asus.com/Motherboards/ROG-STRIX-Z370-E-GAMING/specifications/
You are looking for this part of specification:
Wireless Data Network
Wi-Fi 802.11 a/b/g/n/ac
Supports dual band frequency 2.4/5 GHz
Supports MU-MIMO

A board without wifi will not have such section in its specification.
 
Solution