How to open a file located in a non-sdcard directory in Tasker?
The inbuilt Open File action doesn't seem to work for non-/storage file paths because it is hardcoded (I presumed from its error logs) to only load a file located under /storage/emulated/0. Even if you mention the absolute location using file://, it would still append /storage/emulated/0 to the file path and throw an error. 

Because Open File action simply sends an intent, we can do that manually ourselves. The Send Intent action is pretty good for this, except it also fails with non-/sdcard file paths. Tasker implements FileProvider (a way to securely share files with other apps). The action could work but Tasker's manifest file provisions for not exporting the file provider, which means other apps cannot make use of it. Since Tasker converts even absolute file path (with file://) into a file provider URI, there is no way out for us to load a non-/sdcard file using that action too,  except to ask Tasker's developer to fix this, or the user themselves tweaks the manifest file. 

The solution, however, is available using command-line. Use the action:

Code &rarr; Run Shell:


Command: 

am start -a android.intent.action.VIEW -d "file://FILE_PATH" -t "text/plain" -f 0x13000000 -n android/com.android.internal.app.ResolverActivity


file:// is intended as is. In your case, the file path should be file:///data/misc/wifi/wpa_supplicant.conf.

text/plain can be replaced with text/* too if you don't know your file's mime-type. 

(You can know about am here.) I don't know what that flag (0x13000000) does in particular. 
tick Use Root


Running the task would now give you the bottom sheet with all the apps which can load a file with mime-type text/plain. However, when testing  this, only QuickEdit app was able to load that file successfully, so I recommend using it unless you get this working with an another editor.