How to make TeXstudio recognize \DeclarePairedDelimiter declaration

After the help of @Torbjørn I came up with this workaround.

1. Create a mydefinition.cwl file and place it in the %APPDATA%/texstudio folder (I'm using Windows, don't know where it should go in other operative systems).
2. Add the \DeclarePairedDelimiter{cmd}{left_delim}{right_delim}#md line in the .cwl file.
3. In TeXstudio Options -> Completion check the box of mydefinition.cwl that appeared in the list.

This fixed the problem for me: I get the correct autocompletion for my \abs and \norma commands!

Now a little explaination: as far as I could learn (but if anyone has further information please let me know!), the problem comes from TeXstudio .cwl files, which are not yet complete. There are some packages with some commands which haven't been added to the autocompletion files of TeXstudio yet. The TeXstudio team is working for improving this.