Where are Gradle logs?

View -> Tool Windows -> Build.

There is small "ab" button on the left panel.

All gradle logs for current build are there.

EDIT: There is new icon from AndroidStudio 3.3

Gradle does not redirect its logs in a separate file in Android Studio.

Therefore if you want to view them in a file, you need to build gradle using a command in the terminal and redirect gradle input to a file.

gradlew build > myLogs.txt 2>&1

This command will redirect all standard output and error messages from gradle build to a file called myLogs.txt in the project folder.

gradlew build > myLogs.txt 2> logErrors.txt

This command will redirect all standard output from Gradle logs to the myLogs.txt and all error messages to logErrors.txt

Tested on Windows 10 and works perfectly.

Here is more information about how to redirect standard output from commands to different files.

You can also try running your task like this:

>gradlew --info build

You will get a bunch of useful log information

In Android Studio 4 (at least 4.2.1 now), both the ab button and the Toggle View button (mentioned in another answer) are gone, so Android Studio doesn't show the logs in the Build View anymore, but if a gradle sync fails, there is a button that brings you to view the idea log outside Android Studio (see the right-most button below), entitled "Show Log in Finder" (at least, in MacOS Android Studio).