Gwenview launches without issue for me — launching via the command-line produces the same warning messages you indicated, however it still launches as expected.
Note that many applications may produce warnings when launched from the command-line. This doesn’t necessarily indicate a problem for the User.
As Gwenview doesn’t launch at all for you, then the problem might be elsewhere – one of the first things to rule out is that the problem is due to local configuration;
Please create a new User account for testing purposes, reboot and login to that account, and launch Gwenview normally and via the command-line to see if the problem persists.
Also note any differences in the warning messages that appear, if any. Report back with your findings.
Please provide your system information formatted according to forum guidelines: 
[Mini-HowTo] Provide System Information
Basic details provided by *-fetch type apps might give enough information for someone wishing to buy a computer, however, for Support purposes it’s best to ask your system directly.
Output of the inxi command will generate more useful and detailed information for those who may wish to help:
Suggested inxi command (use either):
|
|
inxi -zv8 |
(short-form) |
inxi --filter --verbosity=8 |
(long-form) |
Command output should be presented as pre-formatted text in accordance with forum guidelines. 
Running inxi within a chroot environment
- Add
--color=0 to the long-form command, or…
- Change the short-form command to
inxi -zv8c0
Your privacy is respected
[Mini-HowTo] Present code or command output
Note: Grave accent (or, backtick) characters are used.
For inline code or to show a single command:
- please follow this simple example:
code here.
For multi-line command output:
- place text beween two rows of three (```) backtick characters to form a scrollable text box, or …
- use the </> button in the Compose window to achieve the same result.
The empty row between these rows of backtick characters is where to paste any multi-line command output (such as inxi).
An example of a pre-formatted text enclosure:
What is a Quark?
A. In Physics, an elementary particle and fundamental constituent of matter.
B. A character from the Star Trek: "Deep Space Nine" television series.
C. A soft, creamy, usually unsalted cheese traditional to central Europe.
