Where do you stop in the Quran?
Wa alaikum assalaam wa rahmatullahi wa barakatuh.
The easiest way to know when to stop is to follow the stop markings over the words in the copy of the Qur'an you are using. The most accurate are those found in the Medinah Qur'an Complex printing of the Qur'an.
The science of stopping and starting correctly while reading the Qur'an is an important aspect of tajweed and one we all should try and study and understand.
To study the complete rules on stopping and starting, please see the following links. The lessons are near the top of the page, where is states Al-waqf 1, al-waqf 2, and on the second link, al-ibtidaa' 1etc. :
Wa assalaam alaikum