Sometimes you need text, rather than voice, output from screen readers. Why? It's really useful for bug reports ("this disclosure icon is announced as 'black dash triangle dash filled dash x2 underscore final dot png' and needs alt text"). Luckily, getting this text is easy to do.
In VoiceOver you press Option + Control + Shift + C to have the last item that was announced copied to the clipboard. Bonus feature: pressing Option + Control + Shift + Z to save the last phrase to the desktop as an audio file.
A three-finger quadruple tap copies the last announcement to the clipboard.
In NVDA you use Speech Output. To get to this, press the NVDA key + N to open a pop-up menu. From there, press T for the Tools menu and S for Speech Viewer. You'll now see a small window appear that contains the text of everything NVDA announces.
In JAWS you use Speech History, which gives a list of the last 50 items that have been announced. To access this, press the JAWS key + Spacebar, then press H.
Open the Global Context Menu by swiping down and to the right. Select the "Copy last utterance to clipboard" option.