you may simplify this task by using the mongodb-slow-operations-profiler tool, open-sourced on github. It is able to show you in a tabular representation all current running operations of one or multiple databases with just 2 clicks. The table is filterable and columns are sortable, so you can easily see the longest running queries, of the namespace you’re interested in, first.
I wrote a blog post about the tool and specifically also about its current-operations-feature: https://medium.com/idealo-tech-blog/practical-guide-to-analyze-slow-mongodb-operations-9363035b01fb#15e2

Have a look, be inspired and simplify your daily work 🙂

Best regards!