Well, a list of all Qt5 devel packages in the configured repos could be obtained with e.g.:
zypper se libqt5*devel
(add ‘-s’ for more details like the version)
OTOH, the naming scheme is consistent anyway.
The devel package for libQt5Xxx5 is normally named libQt5Xxx5-devel.
In some cases, like for libQt5Svg5, the devel package is named after the base package though (here libqt5-qtsvg-devel), maybe because libQt5Svg5 is the only library in libqt5-qtsvg anyway.
PS: You can find the name of the base (source) package via something like this:
$ rpm -qi libQt5Svg5
Name : libQt5Svg5
Version : 5.6.0
Release : 78.1
Architecture: x86_64
Install Date: Fre 25 Mär 2016 18:11:13 CET
Group : Development/Libraries/X11
Size : 511588
License : SUSE-LGPL-2.1-with-digia-exception-1.1 or GPL-3.0
Signature : DSA/SHA1, Fre 18 Mär 2016 23:50:59 CET, Key ID 27c070176f88bb2f
Source RPM : libqt5-qtsvg-5.6.0-78.1.src.rpm
Build Date : Fre 18 Mär 2016 23:49:57 CET
Build Host : build33
Relocations : (not relocatable)
Vendor : obs://build.opensuse.org/KDE
URL : http://qt.digia.com
Summary : Qt 5 SVG Library
Description :
Qt is a set of libraries for developing applications.
This package contains base tools, like string, xml, and network
handling.
Distribution: KDE:Qt5 / openSUSE_13.2