whoamisignedinas

The Google account you are signed in with is normally displayed in the bar at the top right of any Google product window as shown in the top image.

For avoidance of doubt, click on this link>

https://sites.google.com/d/1gMIspJPsKQTwpkNUj17_yrJX8CbFaFr0/p/1CvaaWP_AsR7W2BwVs12XsE_P_wBO1awh/edit

If you are signed in to a google account, you will see the following which will display what Google account you are currently signed in with (bottom image)