I would like to clone my windows 10 from my SSD to my HDD. My HDD has 2 partitions, one with my data and one free. I would like to clone windows on the empty partition of the HDD drive. Can I do that or will I lose my data partition?
Yes, you can, and if properly done, it will work.
Note: Properly means the empty space on the HDD must be larger than the space used on the SSD.
Do you need the whole SSD C: partition space on the HDD or only the actual space that windows takes?
Here's where it gets interesting. There are cloning apps which, on request, will only close active disk sectors to the destination drive. But, then the clone won't be bootable. If you want to be able to boot from the clone, the destination disk must be empty and be the same size or larger than the source drive.
Also, discussing apps and utilities outside of the OS is the province of https://softwarerecs.stackexchange.com and out of bounds here.