I have installed Mikrotik on Virtualbox and I have two interfaces on my computer, LAN and WLAN ( USB Wifi dongle ). I have already internet from LAN but I need to use WLAN ( USB Wifi dongle ) as access point hotspot, how can I do that ?
if that was RouterOS running on the host, and USB dongle had Atheros chipset - you would get the usual wlan interface without any hassle.
In case host system having WLAN and RouterOS running as a guest - configure it on the host and just pass to guest. As i am not sure how well your VMS will forward full hardware handle to guest OS. And this being USB only complicates things.