How to check mfi certification?
Once an accessory has completed MFi certification requirements and is reported to Apple as sold/distributed by the manufacturer it will be searchable in our public database of authorized accessories.
https://mfi.apple.com/account/accessory-search
You can check the MFI certification by Model/Brand/UPC/EA
If you want to get mfi certification for your brand, then you have to work with mfi authorized manufacturers.
If you want to check one cable is MFI or not, you can click this website, and you can find this cable’s brand name/UPC/EAN/Model on the package, normally if it’s MFI certified, you can find this information from their package, cause MFI certified cable have their own packaging artwork requirement, some information you have to put on it as Apple’s requirement.