Using featured image in gridmarket

Hi,
I'm trying to get a featured image to appear above my page title in my child theme of gridmarket. I have the option to set one but when I do so nothing appears.
I do have a custom logo in the header ( i don't know if that's a factor or not). I have tried to mess with the code but only succeeded in doing something horrible that made me need to restore my site (thanks a lot internet).
Any suggestions as to why my featured image may not be showing and what I could do to put an image above a page title.
Thanks
Meriam