Hi, I finished my PCB and I have this warning in the eeschema editor at the upper side. Why does this happen and how can I fix this?
Maybe, open the .kicad_sch with a text editor and search for “space and space”.
It shows 6000 spaces in the editor
What do you mean by “space and space” ?
Search for
quotation mark + space
and for
space + quotation mark
so you can ignore the other 6000 spaces that have no quotation mark around.
Maybe it’s an April Fool’s trick: I say I found something but - hähä - I do not tell you where . Have fun! cynicism off 
I have this message also (Eeschema 9.0.2). I found almost no Google ‘hits’.
I belive it is emitting a warning when any of the fields (like say Datasheet or a user defined field) contain “Value” entries with white space in them.
I can believe this might be a problem for the program logic when dealing with “Reference”, “Value” or “Footprint”. I do not see why it would be an issue for “Datasheet” or user fields.
If it really is a “bad thing to do” then the user should not be allowed to enter white space.
https://github.com/KiCad/kicad-source-mirror/blob/master/eeschema/files-io.cpp
if( schematic.HasSymbolFieldNamesWithWhiteSpace() )
{
m_infoBar->QueueShowMessage( _( "This schematic contains symbols that have leading "
“and/or trailing white space field names.” ),
wxICON_WARNING );
}
Datasheet field usually contains a URL. URLs are not supposed to have spaces. They should be encoded as %20.