The Brainliest Answer!
You can choose any topic for your assembly which will keep the audiences entertained as well as will give valuable tips and points to keep in mind for their whole life. The various topics are
1. never give up
2. confidence and self esteem
3. Discipline
4. about your school
and many others, you can chose any topic but it should be motivating and engrossing 
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welxx!!! mark it as best if u liked it :D
I think, that in your class assembly you have to tell about importance of trees, or freedom fighters!!!!!