In your kali linux, run
apt -y install virtualbox-guest-x11
reboot
On your host, setup something like this
You should now see your shared directory in /media
ls -la /media
If its doesnt work, also run the following.
On your Kali menu bar,
Devices > Insert Guest Addition CD Image
cd /media/cdroom
cp ./VBoxLinuxAdditions.run ~/Desktop
cd ~/Desktop
./VBoxLinuxAdditions.run
reboot