Dear Friends, I need some help.
After I move my files from windows server to the dataset, I lost folder permissions and I can´t set them using chmod.
What can I do in order to get them back?
Do you mean chmod ?
Welcome to the forums.
You would ideally apply permissions via the UI and not the CLI. When you moved these files I assume you ‘preserved permissions’? Windows permissions are not a perfect match with TrueNAS so you may be better to set your permissions on TrueNAS first and then copy the data across ignoring your Windows permissions.
You didn’t lose them. The + means that you have an ACL set. getfacl. chmod isn’t allowed because you have an ACL set. You use setfacl to manipulate ACLs (or use our UI).
As I had many folders under a dataset I thought I could give permission to only this folder that was unset. After all I used the UI to strip ACL and I am applying permissions again. It will take a lot of time. . 
ACLs can be manipulated at any level you want, but once you start making changes it’s hard to undo them without a snapshot.