Hi Andreas,

1. Where can I find the chktexrc-file?

That should live inside of the directory

/usr/local/texlive/2011/texmf/chktex

if you're using texlive 2011, and similarly for 2012 and so forth.

2. And how can I modify it to make ChkTeX ignoring named above warning?

That file looks to be extensively commented. Search for "length of" and it'll take you to the relevant section.

Cheers, Paul