Go to Users -> Resource Policies -> Network Connect -> NC Connection Profiles.
In there edit your connection profile.
In older versions there is a DNS tab, in the latest version it is all in one page.
Set the DNS suffix you want to use under the DNS section.
Then select the radial button to "Use Device's DNS settings then use Client".
Select the tick box to auto-allow IPs in DNS settings if you are using split tunneling and they are not in your routing policy.
Re-connect and it should work.