"If every piece of knowledge is created by combining previous ones, then no true grounded knowledge is possible" - this is not true, and has a very simple solution. What you are calling "grounded" knowledge comes simply from observation.
When the very first human saw that an apple falls of a tree, they have acquired what you call "grounded" knowledge. They can then combine that knowledge with the grounded knowledge that other things fall from trees to start reasoning about why things might fall from trees.
The problem of induction is different. It says, we know that things fall from trees because things have always fallen from trees, but how can be certain that what we call the laws of physics will not arbitrarily change on us?
And of course, it's a famous problem because it doesn't have a satisfying answer. The answer is basically "well everything we know is wrong if induction is wrong, so we will pretend induction is not wrong and hope for the best". And at least so far, that approach has seemed to work (heh heh heh).