Full file names in ES File Explorer
Assuming that ES File Explorer is on default view, which is Large Icon


You can long-press the folder/file, then select More - Properties to see its full name.

For a general way (in case there are many folders/files with long name), you can try changing the view to list by selecting View - (any) List/Detail. In most cases, it will display long enough name. The downside is you only see fewer folders/files.