You have the next:
- Sides JK and LK are congruent:

-Angles MKJ and MKL are congruent:

-Side MK is part of both triangles.
Then, as angle MKJ is between sides JL and MK, angle MKL is between sides LK and MK:

Triangles JMK and LMK are congruent by SAS (side, angle, side)