如何显示 Android 工作室的消息窗口？

It was a bit different in my case. I just closed the Message Tool Window with this red cross on the left and then this window completely disappeared and would not show again even after several rebuilds, View > Tool > Messages Alt+0 was also grayed out. The only thing that helped to bring the Window back is to break the build, so it would be some compiler errors. After that the window has reappeared showing those errors. Now the window is still there, does not vanish. Hope this helps somebody.

Build -> Make Project

(Ctrl+F9 or ⇧⌘F9)

I got here after upgrading to Android Studio 3.1, in which they removed the Messages window, replacing it with the Build window. After some poking around, I found this button on the left side of the Build window:

Clicking this button toggles the view between the new "Build" view and the old "Messages" view.

I hope this helps someone who has the same problem!

UPDATE: per suggestions in the comments, since this doesn't really answer the asked question, I opened it up as its own question: Where is the Messages Window in Android Studio 3.1

UPDATE 2: In Android Studio 3.3 the button now looks like this:

UPDATE 3: In Android Studio 3.6 the button is gone. Instead, the build window is permanently split between text output and visual output. If you can't find the text output, it might be fully collapsed, so look on the top right of the build window for something like this:

And try to drag it left to reveal the build window, like this:

Hope this helps!

Can't find the button @yuval provided, but here it is to toggle to show it

Just to have the whole picture. Go to the Build and then on the left side of the window you will find your Messages icon.