Answer:
1) the sentence “Una merienda ¿Dónde?" means: "A snack, where?"
And this is weirdly written, so it has not a lot of sense but is not written incorrectly, you would say this to invite some one to a snak, and giving him/her the posibilty of choosing the place for it.
2) "Los tunos son músicos que tocan la guitarra y cantan."
The Tunos are usually groups belonging to universities or members of a society that wear old vestiments (That represent their culture and origin ) and do music with string instruments and percussion, so the statement is true.