For those strength exercises where you need to know a percentage of your PR on a movement, you can retrieve that percentage directly from the PR section of your mobile app.
From the Home page in the mobile app, tap the Tracking icon. Then select the Movements tab on the next page. This will put you on the middle screen in the example below.
On the Movements pane, find the movement you are working on today. In the example below, this is the Deadlift. If you have not performed this movement before, it will not be present on this pane (in which case, you can add your results from today for future reference).
To see a list of various percentages on this movement, click on the % icon on the right side of the movement. This will expand the movement line to display the nineteen different percentages from 5% to 95%. Click again to hide.