  Weyl semimetals are characterized by the presence of massless band dispersion
in momentum space. When a Weyl semimetal meets magnetism, large anomalous
transport properties emerge as a consequence of its topological nature. Here,
using $in-situ$ spin- and angle-resolved photoelectron spectroscopy combined
with $ab\ initio$ calculations, we visualize the spin-polarized Weyl cone and
flat-band surface states of ferromagnetic Co$_2$MnGa films with full remanent
magnetization. We demonstrate that the anomalous Hall and Nernst conductivities
systematically grow when the magnetization-induced massive Weyl cone at a
Lifshitz quantum critical point approaches the Fermi energy, until a high
anomalous Nernst thermopower of $\sim 6.2$ $\rm \mu V K^{-1}$ is realized at
room temperature. Given this topological quantum state and full remanent
magnetization, Co$_2$MnGa films are promising for realizing high efficiency
heat flux and magnetic field sensing devices operable at room temperature and
zero-field.
