I want to display replies on discussion topic as a threaded view instead of Flat view. In SP 2013, i see threaded view is available which might do this job but i cant see threaded view in SP 2016. Is there any other way i can achieve this?
Yes, you can get a threaded view. No, you can't get it on SharePoint itself (that I'm aware of).
How can you get a threaded view? My current workaround is syncing the discussion list to MS outlook. Once synced, you can select this list and then click in the menu "view" on "conversation settings", where you can check the box for the "Use classic indented view". Wonder above wonders, you suddenly get an indented ("threaded") view on each discussion.
Added bonus: you can see which items are new (they are marked as unread). No more scrolling through discussions to see from where the new replies start!
The list in MS Outlook stays synced and you can even reply from directly in MS Outlook as well. There is one bug you have to take into account: when you start up in the morning, it's possible Outlook doesn't sync the discussions. According to our IT department, this has something to do with the authentications, but it's not enough of an issue for MS to solve as you can simply close Outlook and restart it and the syncing works for the remainder of the day.
If you want to get a threaded view on SharePoint instead, I suggest you vote for this feature on UserVoice.