Catalpa speciosa - multiple trunks
Multiple trunks sometimes develop in response to root crown damage.
The photo doesn't show the entire clump, so take that into account when you consider the following:
Generally speaking, tree care experts discourage pruning out more than one third of a tree or shrub's stems or branches in a given year.
So far as we can tell from the photo, the trunk at the right appears to be the largest and tallest of the three. If so, preserve it and remove the other two in stages. The trunk farthest left shows recent damage near the root crown. Remove that one now. If the largest trunk grows normally this growing season, remove the last extra trunk in late winter or early spring 2019.
In the meantime, protect the primary trunk from abrasions or other damage.