I've install the "Ask Ubuntu Lens" from the software center but it didn't show up is the lenses and I can't search for it as an install app ! What should I do ?
Did you try to re-boot your pc and check for Ask Ubuntu Lens, if it doesn't work even after a reboot, Try to remove Ask Ubuntu Lens from Terminal and install it via the Terminal.
Try this with Terminal.
sudo add-apt-repository ppa:askubuntu-tools/ppa
sudo apt-get update
sudo apt-get install unity-lens-askubuntu
Further details on the installation are here - How do I install the Ask Ubuntu Unity Lens, and how do I use it?