How do you indicate congruent angles in a diagram?

Answer 1

.. by marking the equal angles using the same symbol.

Sometimes a small letter like x or o is used, other times I have seen an arc drawn in each of the equal angles, a double-arm arc for the second set of equal angles etc.

As long as you use a unique symbol, all is fair.

Answer 2

yes

Answer 3

by using dashes on side lengths and/or same number of arcs in the angles