The Boot drive would be C. And if you go to the support page for your system, you did not post the exact model number, the spec page will generally indicate which drive is Boot and therefor which is C. Also if you click on File Explorer, This PC, you can clearly see which drive is C and by clicking on the C drive you will see the Windows folder (which is boot).
I am somewhat new to this and this is probably a dumb question but for the life of me I can't find out which drive is which.   I bought a new Alienware Desktop this week and I can't find where each hard drive is labeled which one is c and which one is d. Mine has both: 1TB M.2 PCIe NVMe SSD (Boot)  1TB 7200RPM SATA 6Gb/s (Storage) I'm assuming PCIe is C and the SATA is D but I can't find it for sure. Also everything saves by default to see, even pics and things. Is that the way it should be?
Dual Drives