Abstrakt: In this talk three different studies we have undertaken to address cosmological issues, like dark energy, will be presented and their results will be discussed. In these studies we have tried to remain model agnostic as much as possible. In particular, our first study (arxiv:1902.11051) concerns a cosmic fluid obeying rest-mass conservation of unspecified equation of state (EoS) in an unspecified background assuming just that the fluid's speed of sound is positive and less than the speed of light. Our second study (arXiv:2001.00825) performs a dynamical analysis of a barotropic fluid of unspecified EoS with positive energy density in spatially curved Friedmann-Robertson-Walker (FRW) spacetimes. While, the third study (arXiv:1905.08512) performs a dynamical analysis of a broad class of non-minimally coupled real scalar fields in spatially curved FRW spacetime with unspecified positive potential.