How do I find out the actual transaction fee for each of these settings?

The exact Jaxx miner fees vary per transaction depending on various factors. You can still get an estimate for each "Fast", "Average", "Cheap" option.

Steps

1. Using Jaxx app, at the top of the screen, tap/click the appropriate cryptocurrency symbol presently activated. Such as BCH (Bitcoin Cash) or BTC (Bitcoin). In this example we will use BCH.
2. Navigate to Menu >>> Settings. Tap on “BCH Mining Fee” option.
3. Select one of the following three options:
   1. Fast
   2. Average
   3. Cheap
4. Still using Jaxx, start a BCH transaction. After you tap "Send", a small orange confirmation screen will mention the exact fee you will pay to the miners before you can confirm the transaction. This is your first answer.
5. To get all your answers, repeat all of the above steps for "Fast", "Average", "Cheap" option.
6. Done. Now you know the exact estimated fee per option. Enjoy :)

Notes

• Jaxx said that they are using adjustable fees based on a feed from https://bitcoinfees.earn.com and they are adjusted based on the historical fees charged by the miners in the past few blocks. Source at https://www.reddit.com/r/jaxx/comments/6u0p06/what_is_jaxxs_mining_fee/dlpdz1z/

• There are three levels of miner fees you can choose from. They determine the speed of the transaction to be confirmed by the network. Three level:

  1. Fast
  2. Average
  3. Cheap