I was wondering what is the dynamic range of an HDR photo if the bracketing was set at 2EV? (in F-stops)
HDR does not extend the dynamic range of a photo. It compresses the extended dynamic range into the same dynamic range limits (display/print reproducibility).
Technically dynamic range is the difference between min/max; i.e. contrast. That is always the same (black and white) as limited by the display medium.
Tonality is the measure of the number of tones that fall w/in the min/max values. Which is why HDR is also referred to as "tone mapping;" because it rewrites the values to fall w/in the min/max.
There are also limitations as to the file format and gamma curve applied. i.e. an 8bit jpeg w/ 2.2 gamma curve can show about 12 stops of tonality; whereas a 14bit encoded raw file with a 1.0 gamma applied can show 14 stops of tonality.
And then there are the limits of the camera in use, as well as the scene being recorded. I.e. how much dynamic range and tonality was actually recorded in each image, and how many images are being combined/compressed?
I don't believe you understand the question you're asking, but that's OK.
I'm assuming you've taken some guesses here about daylight range of 13 'stops', the eye's visible range, and wondered how an HDR photo with a +2 'stop' of intensity would work.
Well... if you think in 'stops' (for photos) then it becomes pretty easy- it's 15 stops. If you go +2, you get 17 stops.
Film is pretty forgiving but I believe 13 stops was pretty easy to do with good processing, and if you worked hard you might get slightly better.
I agree with @J.Hirsch answer. If you have an additional bracketing +2EV you have 2 stops more range than the previous one.
But you need to take into account that an HDR Image must be saved in a special format, normally a floating-point file format, then the file itself has now space to hold a lot more dynamic range, but if it is used or not is beyond the point.
If the second image you capture has the same information you already captured with the previous image, you probably will not get any additional information.