If SDK folder is present in system, one can find in C:\Users\%USERNAME%\AppData\Local\Android
If Android/SDK folder is not found Once done with downloading and installing Android Studio, you need to launch studio. On launching Android studio for the first time, we get option to download further more components, in that we have SDK. On downloading components one can find SDK under Appdata (C:\Users\%USERNAME%\AppData\Local\Android)