(i) Why do predictions of helioseismology disagree with
those of the standard solar model?
(ii) What is the solution to the lithium problem in Big Bang
nucleosynthesis?
(iii) What do the observed light-nuclide and s-process
abundances tell us about convection and dredge-up in
massive stars and AGB stars?
(iv) What are the production sites of the gamma-ray emitting
radioisotopes 26Al, 44Ti and 60Fe?
(v) What is the origin of about 30 rare and neutron-deficient nuclides beyond the iron peak (p-nuclides)?
(vi) What causes core-collapse supernovae to explode?
(vii) What is the extent of neutrino-induced nucleosynthesis?
(viii) What is the extent of the nucleosynthesis in proton-rich outflows in the early ejecta of core-collapse supernovae?
(ix) What are the sites of the r-process?
(x) What causes the discrepancy between models and observations regarding the mass ejected during classical nova outbursts?
(xi) Which are the physical mechanisms driving convective
mixing in novae?
(xii) What are the progenitors of type Ia supernovae?
(xiii) What is the nucleosynthesis endpoint in type I x-ray
bursts? Is there any matter ejected from those systems?
(xiv) What is the impact of stellar mergers on Galactic
chemical abundances?
(xv) What are the production and acceleration sites of
Galactic cosmic rays?
There are plenty of open questions, and that is nice as it gives opportunities to make contributions.