X1 uses Oracle "Outside In Technology" (formally Stellent before acquired by Oracle) for the data extraction and viewing and thus is constrained by the formats supported by "Outside In Technology".
The list of supported formats are at: Supported Formats.
It lists OneNote as: Microsoft OneNote (text only) 2007, 2010, 2013. This means X1 should index text in OneNote but not view it.
The list of supported formats are at: Supported Formats.
It lists OneNote as: Microsoft OneNote (text only) 2007, 2010, 2013. This means X1 should index text in OneNote but not view it.