I love his beautiful eyes so much! 
I’ve learned a lot since I fell down the dog breed research rabbit hole!
#1 lesson: be prepared to be surprised. Or not! 
One of the most important things I learned is how easy it seems, but how hard it is, to visually identify the breed traits in a mixed breed. Because of the way genetics work, and especially in dogs: Dominant genes that hide other traits, recessive genes that don’t show the trait, incomplete dominance that change what we see, genes that act on other genes to change the outcome in the actual dog, etc. and so on. As with many before and after me, I learned that I’m not nearly as good at identifying the breeds in mixed breed dogs as I thought! 
I definitely see some potential GSD traits in your handsome dog. And yet, those traits can be misleading, as well. As well as his juvenile self not yet showing his final self version.
Many breeds have prick ears. He’s a useful shape for his size, as are many breeds and mixes. And his coloring may trigger GSD impressions but is actually one of the “generic” primitive dog color & patterns – brown with black saddle, with or without black masking on the face. Sometimes very-mixed breed dogs with no GSD have a similar coloring and pattern.
(Found this bit of trivia so interesting: Most GSD’s are in the primitive color / pattern range because they are one of the earliest ‘breeds’ developed by humans living in wild country in Europe. Ancient humans who desperately needed a guard / livestock dog. This lot of hang-around dogs virtually volunteered for the position in exchange for food. Somewhat similar types can be found throughout central and eastern Europe.)
My all-time favorite sub-Reddit, at times profoundly educational, although sometimes you have to sift through the chaff:
https://www.reddit.com/r/DoggyDNA/
If your dog has lifelong “sonar ears” you might enjoy this sub-Reddit for dogs who may involuntarily take flight in a high wind (jk! sort of).
https://www.reddit.com/r/sonarears/
y’all look … my favorite ever sonar-ear dog … I don’t know if anyone has measured yet, but there may be more ears than dog …
https://www.reddit.com/r/sonarears/comments/1j0ie8f/hairy_sonar_ears/