Recently I found myself in a strange situation, where I was searching for a certain document located on my NTFS Data partition, but Spotlight wasn't able to find it.
I have Paragon NTFS for Mac installed, and I thought that with this Spotlight could understand NTFS, but it didn't.
With a tool called
mdutil you can check if indexing is enabled on a specific partition or drive.
mdutil -s /Volumes/DRIVE_NAME
-s stands for status, so check if indexing is enabled on your desired partition:
To turn indexing on just run the following command:
sudo mdutil -i on /Volumes/DRIVE_NAME
Good, now the only thing left to do is rebuilding the index.
To do that simply run this in your terminal:
mdutil -E /Volumes/DRIVE_NAME
Now either restart your system or wait until Spotlight schedules a new index refresh.
Ale Mello suggested to the following method:
In your System preferences navigate to Spotlight > Privacy
Add the drive you want to be indexed by Spotlight (if already in the list, remove and then add the drive)
Spotlight will now reindex the drive.