As mentioned there is no automatic extraction of the average, so you will have to settle on eye-balling it from the curves passing at a point or doing the computation by hand or in a spreadsheet. Min and Max can be read on the plot.
I need the angle value when the leg is in 6 oclock
Do you mean when the leg is vertical or when the crank is vertical and the pedal is at the 6 o'clock of the sprokets?
There is a tool for "angle-to-vertical" but unfortunately it is not usable with the angle-angle diagram at the moment.
There might be a simpler way to do this with a custom tool and I'm not an bike fitting expert so please take the following as inspiration only.
If you can show how you normally measure it for a single cycle maybe I can come up with a better solution.
You could add a regular angle tool to act as a reference for when the pedal hits the 6 o'clock mark. Set one of its leg horizontal and the other vertical, with the end of the horizontal leg tracking the pedal or a marker on the foot, aligned with the pedal, and the other two points placed in such a way that the background behind them will not change. This way the angle is always less than 90° when the pedal is up, and 90° when it's at 6 o'clock.
Then add another angle for the knee joint angle.
Something like this:
The blue angle will act as a reference. It will read 90° when the pedal is at 6 o'clock and less than 90° otherwise.
You track these for a while: right click on each angle and do "tracking > start tracking", then progress frame by frame verifying that the auto-tracking is solid and adjust it along the way when necessary, then "tracking > stop tracking" when you are done.
Then go to Tools > angle-angle diagrams, and you should get something like this:
If you look at when the reference angle (X-axis) is at 90°, you can see that the knee angle is around 118 to 120°.