I have a document in RGB color space, to prepare graphics for a printing house I need to replace RGB with CMYK color space. How do you do it in Inkscape?

Still via Scribus, AFAIK.
http://libregraphicsworld.org/blog/entry/getting-cmyk-colors-from-inkscape-to-scribus

TD

So does the CMYK color option in the fill and stroke panel not actual usable for printing?

Bwimb87

So does the CMYK color option in the fill and stroke panel not actual usable for printing?

Not directly from Inkscape, no. It will write CMYK values to the file, and the file can be taken to other programs like Scribus for printing.

Hello,

To print the files I have, they ask to have ai format. In this case is there a workaround to keep the colors as CMYK in the file? I am quite new on inkscape sorry if my question is inconvenient. 

Regards