Thanks for your question and the photo attachment! There are a number of serums compatible for microneedling treatment. The kind of serum needed for your scar will depend on the overall goal that you want to achieve as well as the depth of the scars that needs healing.
As for your case, just basing on the photo that you have provided, Vitamin C will work, but I would suggest an additional serum to get better results. This serum such as a Growth Factor is a safe and effective product for healing facial scars. Vitamin C, on the other hand, is a good antioxidant and could be helpful in building up collagen. During the microneedling session, Growth Factor could be applied and after the treatment is done, you can apply both Vitamin C to get the best results. Depending on your final assessment, your doctor could recommend a number of treatments to start seeing results.
Go and see your doctor to have your case evaluated. Your doctor should also be able to help in determining the number of sessions needed as well as if there are other products that should be used for your scars. Good luck!