Explanation:
you should have measured the lengths of the sides and added that information here to the picture.
because we here cannot measure this from a picture that is inclined and has no size scale.
I can give you a hint how to get the angles, when you have all 3 sides :
start with the extended Pythagoras for non right-angled triangles:
c² = a² + b² - 2ab×cos(C)
with c being the side opposite of the angle you are aiming for.
then
2ab×cos(C) = a² + b² - c²
cos(C) = (a² + b² - c²)/(2ab)
for example, to get the angle at T, its opposite side is SE.
cos(T) = (ST² + ET² - SE²)/(2×ST×ET)
you can do the same thing for all 3 angles (you need to always pay attention to what sides you have to use in what combination for the angle).
or you can switch after getting the first angle to the laser of sine :
a/sin(A) = b/sin(B) = c/sin(C)
where the sides and the disposing angles are always opposite of each other.
for your triangle that looks like
ET/sin(S) = ST/sin(E) = SE/sin(T)
from there (once you have one angle via the Pythagoras approach) you get all other angles.