Um having problem with software center in Kubuntu 15 plasma. um using ethernet connection and can surf internet through firefox but um not getting connection in software center

Moved to Systems & Utilities - did not belong in Forum Feedback

Software Center - you mean Muon? SW Center is a Ubuntu GTK (Gnome) app

is this a new install?
did it ever connect?
do other apps have issues connecting to the net?

Are you using a proxy maybe?

Could be this bug that should be fixed in KDE Frameworks 5.15:
https://bugs.kde.org/show_bug.cgi?id=350890