@frederick_jfg I hate to be the bearer of bad news but there are really no common parts with this. Virtually any part can have failed because of the water damage. For now, stop trying to charge it, to turn it on or to do anything with it. that could potentially make bad things worse.
The very first step I would take is to disassemble your iPad. Use these guides iPad mini 4 Wi-Fi Repair to help you disassemble your iPad. Take a careful and close look at all components and connectors. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. You will have to remove all the EMI shields. If you do not remove the shields, you are not cleaning the board. Once you got the gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for an Apple iPhone 3G but it is still pertinent to your iPad as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. Do not use compressed air for the cleaning since that can drive liquid as well as corrosion particles into areas that will cause trouble later on. Do not use drinking water, if you need to use water, use sterile water. Also, you do not need to leave it to dry for a day. Isopropyl alcohol in the higher concentration will evaporate quickly and dissipate the water. The importance here is the cleaning. It would of course be best to get it professionally ultrasonic cleaned Do not forget to replace the battery. This is a must and not an option. It will fail if you do not take care of it now. After that, reassemble your iPad and re-evaluate. For as long as you have not cleaned your board and replaced the battery, everything is just a guess. Keep in mind that water damage is the hardest to troubleshoot and to repair. It does not matter if is was exposed for 2 seconds or 2 hours, what matters is where the water (particulates) did the damage.