First of all, Enotes offers many varied activities and lesson plans on Shakespeare's Macbeth of which you may wish to afford yourself. Then, regarding contextual questions for eighth-graders, you will, of course, wish to direct these questions on the aspects of the play that you have emphasized. In addition, you will wish to direct questions to the level of your students' abilities.
Since eighth-graders have read Macbeth, the assumption must be made here that these are high-functioning students, perspicacious enough to understand nuances of character and theme. Therefore, the Lesson Plans that you can access from this site should serve you well as you can select from the various tests questions appropriate to your discussions and the functioning level of your students. So, please see the links below as well as go to the "Lesson Plan" tab on the Macbeth Group site, the site that this question is under. And, thank you so much for using Enotes.