You most likely never will be able to. Do you know what the glue was? Solvent may help but typically old adhesive like that is scraped off.

I would try heavy duty paint stripper and a wire brush with a 20% chance of success.

Hammer and small sharp chisel to start.

I had to do something like this years ago - my memory is making sure the remover solvent (whatever you choose) sits on the glue for a few hours - here's something to try that I pulled from DIY site that explains this somewhat

"The thing is you need to let the solvents soak into the brick. *Test this on a small area before tackling the brick as it may darken the area... soak bandage strips in the solvent (wearing gloves) and using Gorilla tape adhere it to the strip. Then cover the strip with plastic and tape that up. Give it at least 2-3 hours to soak in, then remove the strip. Keep doing this until completely gone. I use marine strippers for all my heavy-duty stripping/removal needs. Just don't get it all over the brick."

Ughh!!!

Exposed brick does not make a great backsplash either, remember that they will need to be cleaned and spatter may not some off any easier than the current glue.

I wouldn't want a brick backsplash, either, for the reasons MWM cited.

As to removing the glue--looks like Liquid Nails or something similar, I would try dry ice & chip it away bit by bit before resorting to any solvents/ paint removers. Because I would be afraid that dissolved/ dissolving glue/ solvent would soak into the brick & be more unsightly than it is now.

https://www.finehomebuilding.com/forum/removing-liquid-nails