I'll answer one by one so you don't confuse them. Also no problem, my profession is teaching so I am patient with everybody
1. I can't be hundred percent sure if Assisted GPS and WLAN scanning is present as an option in Global Rom but on EU Rom its in:
Passwords & Security > Location > USE ASSISTED GPS (bottom of the page)
Passwords & Security > Location > SCANNING > WLAN SCANNING (untick it)
You can use the search feature in your settings to find it (if it is available.)
What USE ASSISTED GPS does is, it uses your mobile data to confirm your location. It constantly does this so when you have a GPS requiring app on like Maps, your battery dies faster as it also checks in the background to confirm your location. You do not need this as 1, your mobile service takes care of this automatically and 2, the GPS in your phone is accurate enough (especially on Mi 9 with dual GPS)
What WLAN SCANNING does is actually misleading. It doesn't scan for wireless signals so that you can connect. It reads "Allow apps and services to scan for Wlan networks at any time EVEN WHEN WLAN is OFF. This can be used to improve LOCATION BASED FEATURES AND SERVICES". So when you are using maps and you have your WLAN off, you phone is still looking for WiFi signals to confirm your location. Again, you don't need this. Your phone will take care of it anyways.
Turn both these down and you'll see that your location information is just as correct as before. The only catch is, you get more battery life. I noticed this significantly as I was wondering around my city last weekend.
2. Pinging emergency services are related to your GSM signal band so WCDMA/LTE, not the other two.
3. Here is the tricky part. I plan and am using only 1 sim on my Mi 9, I don't another sim card and don't plan to get one. I tried turning my second sim off, you have an option in the menu I told you. But if you turn it off, you lose signal completely on your first sim as well. So that option is not going to work. I decided to turn the second, unused sim to look for the least demanding signal band but again, if you change it to something other than what the other sim is looking for, you'll lose signal again. So in short, you have to choose the same signal band for both sims.
The reason I'm telling you this is, you are just making your phone to specifically look for WCDMA (3/3.5) and LTE (4/4.5G). If your phone can't find any of those, let's say that you are in an accident and clicked emergency call, your phone will send SOS signals through all band frequencies starting with the one you preferred. Since every city has 3G, even in the least advanced city you'll be pinging SOS through 3G in less than 5 seconds. Starting from LTE, to WCDMA, CDMA and etc.
In conclusion, there is nothing to worry about. Emergency service feature on phones works slightly different than usual GSM stuff. Should you need it, the setting I told you won't affect the results. However it will prolong your battery life. Trust me, when you are forcing your phone to look for WCDMA/LTE and when one of the SIM cards actually gets a hold of the signal, your battery will stop draining. Before I changed my setting, my sim1 was on Auto and the sim2 was on bands that consisted all of the signals. That was killing my phone even when it was just sitting on the table.
