What is this part which is mounted on the wing of Embraer ERJ-145?
They are called vortilons. They can induce a vortex to the upper surface of the wing at high angles of attack, which allows flying at higher angles of attack before stalling.

Additionally, four vortilons were installed on
the lower surface leading edge of the outboard wing panel. Their interaction with the wing sidewash at high angles of attack produce
strong vortices that are convected to the upper surface, where they
modify the pressure distribution and boundary layer development,
postponing flow separation and increasing maximum lift. Their
shape and position were defined using the 3D panel program. The
combined effect of the leading edge droop and vortilons allowed an
improved take-off and landing performance without resorting to
more complex variable geometry leading edge devices (such as
slats), for a small cruise performance penalty. Figure 22 shows a
schematic representation of the ERJ145 droop and vortilon.


(The evolution of the aerodynamic design tools and transport aircraft wings at Embraer)
They were first used on the Douglas DC9. The original patent shows the vortex on the upper side of the wing: