The WFIRST's study of dark energy is pretty straight forward. It's no different than the previous ways of studying dark energy. It's not studied directly, cause we can't see it or re-create it, it's studied by the effect it has on the relative motion of distant galaxies.
WFIRST will get much more accurate readings on the relative velocity of galaxies both relative to each other in their neighborhood and relative to us, this will get a significantly more accurate estimate for dark energy than was previously possible and questions can be answered such as, is it speeding up.
NASA's WFIRST Web page discusses this in more detail
The High Latitude Spectroscopic Survey will measure accurate distances
and positions of a very large number of galaxies. By measuring the
changes in the distribution of galaxies, the evolution of dark energy
over time can be determined. The High Latitude Survey will measure the
growth of large structure of the universe, testing theory of
Einstein's General Relativity.
Type Ia Supernovae (SNe) Survey uses type Ia SNe as "standard candles"
to measure absolute distances. Patches of the sky are monitored to
discover new supernovae and measure their light curves and spectra.
Measuring the distance to and redshift of the SNe provides another
means of measuring the evolution of dark energy over time, providing a
cross-check with the high latitude surveys.
High Latitude Imaging Survey will measure the shapes and distances of
a very large number of galaxies and galaxy clusters. The shapes of
very distant galaxies are distorted by the bending of light as it
passes more nearby mass concentrations. These distortions are measured
and used to infer the three-dimensional mass distribution in the
Universe. This survey will determine both the evolution of dark energy
over time as well as provide another independent measurement of the
growth of large structure of the universe.
Dr. Yun Wang's comments appear to be written for a Science-TV show and/or youtube video, and video like those are designed for a general audience so I wouldn't analyze that particular sentences meaning too closely.
As for Erik Verlinde's . . . ideas. I'm not a fan of his proposals, but the answer is mostly the same. WFIRST will get more accurate readings and better readings should help get more specific answers.