where should I put qwt plugin on linux?

[Uwe]

Are you just saying to install my distro's qwt package? I already did that...

Of course you also have to use the Qt packages of your distro - instead of installing the SDK manually !

But when you really need to install Qwt yourself read the INSTALL file. It explains how to configure your environment, so that the plugin is loaded from where it is installed.

Uwe