You open the HTC One A9s from the front. The screen is glued down with adhesive. I recommend using an iOpener and a set of Opening Picks. Here is a YouTube video detailing the repair: https://www.youtube.com/watch?v=qSWMFBcW...
To identify the short, you need to test each component individually. Most motherboards have obvious traces that you can follow to each component. If you can get a part number off of a component, you may be able to look up it’s resistance and voltage requirements.
Hi Robert, When you replaced the screen, did you transfer the home button from the old screen? If not, that is why Touch ID is not working. You may need to reseat the home button connector, as it may not be making a good connection. To be honest, I’m not sure about the force touch. I’ve never had that issue. Maybe someone with more experience with that issue can help shed some light on it.
Any time a device with adhesive is taken apart, the adhesive should be replaced if possible. However, in this case, it appears that iFixIt does not have the adhesive. Most of the time, the adhesive is just used as a water barrier and isn’t actually used for holding the front cover on. I would look and see if you can find the adhesive somewhere (possibly ebay), but if not, it shouldn’t be that big of a deal.