Ammon’s question, “can ye tell” is rhetorical. He knows that his brethren understand their blessings. “Tell” refers to pronouncing them, not recognizing them. Indeed, the purpose of this discourse is precisely that: to give utterance to those blessings.
For Ammon, as well as for us, putting our blessings into words solidifies the experiences and helps us locate them more firmly in memory. The process of stating forces us to organize events in our mind and establish the links between our memories and our feelings about those memories. This is one of the functions of bearing testimony; it organizes our feelings about the gospel into more solid structures that are more tangible to memory. By stating our experiences, they become even more real.