After the next production release goes live (Saturday, February 20th, 2016), you'll be able to see whether your students are viewing feedback you leave using Speedgrader!
Whenever you use Speedgrader to annotate your students' work or leave comments, they should click "Grades" in the course navigation menu on the left, then click "Preview" after selecting the proper assignment. When they do this, they'll be able to view the annotations you've made in the margins of their work.
Instructors will now be notified that students have clicked "Preview". This is a good way to ensure that students are receiving the feedback you leave.
If you'd like to incorporate this feature into your assignments, feel free to contact an instructional designer by writing firstname.lastname@example.org. You may also be interested in registering for an upcoming workshop on Using Grading for Learning and Assessment (DCAL, March 16th, 12:30-2:00 pm). Click here to register: http://libcal.dartmouth.edu/event/2285101