  We present and analyze a near infrared(NIR) spectrum of the under-luminous
Type Ia supernova SN~2020qxp/ASASSN-20jq obtained with NIRES at the Keck
Observatory 191 days after B-band maximum. The spectrum is dominated by a
number of broad emission features including the [FeII] at 1.644mu which is
highly asymmetric with a tilted top and a peak red-shifted by ~2,000km/s. In
comparison with 2-D non-LTE synthetic spectra computed from 3-D simulations of
off-center delayed-detonation Chandrasekhar-mass white-dwarf(WD) models, we
find good agreement between the observed lines and the synthetic profiles, and
are able to unravel the structure of the progenitor's envelope. We find that
the size and tilt of the [Fe II] 1.644mu-profile (in velocity space) is an
effective way to determine the location of an off-center delayed-detonation
transition (DDT) and the viewing angle, and it requires a WD with a high
central density of ~4E9$g/cm^3$. We also tentatively identify a stable Ni
feature around 1.9mu characterized by a `pot-belly' profile that is slightly
offset with respect to the kinematic center. In the case of
SN~2020qxp/ASASSN-20jq, we estimate that the location of the DDT is ~0.3M(WD)
off-center, which gives rise to an asymmetric distribution of the underlying
ejecta. We also demonstrate that low-luminosity and high-density WD SNIa
progenitors exhibit a very strong overlap of Ca and 56Ni in physical space.
This results in the formation of a prevalent [Ca II] 0.73mu emission feature,
which is sensitive to asymmetry effects. Our findings are discussed within the
context of alternative scenarios, including off-center C/O detonations in
He-triggered sub-M(Ch)-WDs and the direct collision of two WDs. Snapshot
programs with Gemini/Keck/VLT/ELT class instruments and our spectropolarimetry
program are complementary to mid-IR spectra by JWST.
