As you know, the Challenger does not have a transmission dipstick. That is because the system is sealed and Dodge does not want incorrect fluid to be added to the system. So dealers use a special StarScan tool to properly assess the fluid level. If, however, you want to check it yourself, this video describes the complicated process. By the way, the fluid for an 8-speed transmission costs $43 per quart and a flush would cost $850 (9 quarts x $43 plus labor).
Valvoline ATF-4 sells at Walmart for $9 qt and is used commonly without issue. BMW and many others require the very same ATF change process and also do not use a dipstick (I recently did my BMW with a Valvoline synthetic). The filter in many of these applications is incorporated in the pan and the new pan with filter will also come with new bolts (those so inclined can go further with what they want to replace while in there). This is a good example of the manufacturers simply making it more difficult for us to perform our own maintenance so they can do it.
Noted today while changing engine oil my 2010 R/T does have a trans tube, the top of which has a cap and is positioned in engine compartment closer to firewall. The cap reads 'for dealer use only' so it appears the dealer may be able to insert a measuring stick into the tube and may also use the tube for refill purposes (which is much easier than pumping fluid in from below as is required with BMW). The Nissan Rogue has the same trans tube (w/out dipstick) and it's used for refill (much easier than pumping fluid into trans from below until it begins to escape as is required with BMW). Someone on youtube figured out that a dipstick could be made with fibreglass pallet strapping cut to a specific length after determining the length required when known to be full. Anyone motivated enough to want to could determine appropriate length for a Dodge for checking fluid level (may have already been done but I haven't searched to know).
https://www.amazon.ca/Automatic-Tra...fix=dodge+auto+trans+dipstick,aps,195&sr=8-20 Member 'Niles' discovered these on Amazon! Who knew?
Read the reviews. Buyers say some are too short and others too long. If you do not know if your transmission is properly filled, how would you know it's accurate or not?