One of the factors which may make speech and language therapists less likely to work with the trans community is the number of possibly unfamiliar terms. Here is a brief introduction.

Tips for Allies of Transgender people
Read this information produced by GLAAD

Born this way? Cis and Trans

Cis and Trans are Latin terms meaning 'same' and 'opposite'.

Cis means that your gender matches the sex you were assigned at birth. I am therefore a cis male.

Trans means that your gender is different from the sex assigned at birth.

Gender is a social construct, while sex is biological.

Pronouns

We all have pronouns. They are not our preferred pronouns, they are just the ones we always use.
As a cis-male, my gender is male and my pronouns are he and him.

The best to way to establish someone's gender and pronouns is to ask them. Tell them yours as well!