By default it should be stored in temp folder.
Try %temp% in run command and check whether the screenshot is taken. Please check the documents,
- default temp location storage.
'Take screenshot after logging in'
WebUI.takeScreenshot()
- custom location store.
'Take screenshot after logging in'
WebUI.takeScreenshot('E:\\screenshot.png')
- relative path storage which will be stored under your katalon studio folders in tests explorer.
'Take screenshot after logging in'
WebUI.takeScreenshot('Test/Demo.png')