iOS11 beta 2

iOS11 bate 2

Apple will release a new Beta when they are ready to release it. It really depends on what bugs they find and fix so it could be 1 week, 2 weeks, or maybe three weeks.

LAst year it was July for beta 2 I think. About 5 or 6 before release.

PUblic beta about beta 3 or 4

/guessing

How we will get an update for beta 2

There were 8 developer betas of iOS 10 and 7 public betas. To answer OPs question usually what happens is beta 2 will be released on the same day as the public beta however it is possible they could release beta 2 as early as tomorrow because (as you may have seen on the forums) Vodafone UK completely bricks devices on the beta.

Either Via OTA or downloading the firmware and using iTunes or Xcode to install it on to a device.

Same as always.

Also regarding beta releases. Normally I've found that they release a new beta every two weeks. Though the gap between the first beta and the second is sometimes longer.