I suppose this is not so much about knowing where in that single file each individual episode starts but about how those multi-episode files are displayed inside the user interface. Plex gives no indication to the average user that an episode item is part of a group of episodes merged in a single file.
Apparently Emby is displaying this differently. While I have no personal experience with it, I assume it’s kind of how Apple’s “Photos” is displaying a “heap of pictures” in a multi-select situation (same as Finder w/ files) – not sure if this includes the UI “merging” the single episode’s titles and descriptions.
In my own library, the few multi-episode files left are mostly season finales… in which case it’s easy just to keep Plex believing it’s actually a single episode (dropping the final file which most often shares the episode title).
Just did a search – it seems to be as simple as displaying 1 item per file and showing a combination of that files information, e.g.
| Property | Value |
|---|---|
| Identifier | S1, E1-2 |
| Title | <Episode 1 title> & <Episode 2 title> |
| Description | ` |
TL;DR
There used to be a feature suggestion describing this behavior. It’s closed as “implemented” (maybe for a subset of the feature; I didn’t follow the complete 95 posts) – despite that there’s still quite a number of votes connected to it. Let’s keep this similar request open until we’ve been able to investigate the “odd status” of that other suggestion 
