How do I determine which iOS SDK I have?

If you type this:

$> xcodebuild -showsdks

it gives something like this:

$> OS X SDKs:    OS X 10.8                       -sdk macosx10.8    OS X 10.9                       -sdk macosx10.9iOS SDKs:    iOS 6.1                         -sdk iphoneos6.1    iOS 7.0                         -sdk iphoneos7.0iOS Simulator SDKs:    Simulator - iOS 6.0             -sdk iphonesimulator6.0    Simulator - iOS 6.1             -sdk iphonesimulator6.1    Simulator - iOS 7.0             -sdk iphonesimulator7.0

If you care about the build number (like "10B61"), especially during betas, the best place to check which version of Xcode and related SDKs you have installed is to use "System Information".

Apple Menu > About This Mac > System Report > Software > Developer

Once there, you'll see version and build numbers for all of the major components of the Developer Tools. The top level version and build number corresponds to the name of the disk image you downloaded from Apple.

This is as of macOS 10.14.3.

For latest version of MAC OS Mountain lion:

Apple Menu > About this Mac > More Info... > System Report... > Software > Developer

You will find Developer information like this:

Version: 4.6 (4H127) Location: /Applications/Xcode.app Applications: Xcode: 4.6 (2066) Instruments: 4.6 (46000) SDKs: OS X: 10.7: (11E52) 10.8: (12C37) iOS: 6.1: (10B141) iOS Simulator: 6.1: (10B141)