These questions are designed to help keep missionaries in the field by moderating the kinds of help the church offers them during their service.

noticeable speech epidiment

Your bishop wants to know about your speech impediment so that the MTC's speech therapists can offer you missionary-specific help when you're at the MTC.

ADHD (not to mention anxiety)

I don't know you. I don't know your heart. I don't know what you have and haven't done in life, so I won't say anything about whether you have a call or not (except that you might consider that both Enoch and Moses had speech impediments).

However, I can definitively say that it is extremely common for otherwise worthy missionaries who are taking medication to control the symptoms of problems like ADHD and anxiety (and depression and asthma and IBS and a whole host of other possibly debilitating conditions) to:

1) go into the field without fully disclosing the extent of their problems

2) stop taking the medication

3) and then experience the full weight of their condition in a context where no one knows what is going on.

This breakdown is, as you might guess, very disruptive. It disrupts the missionary, their companion, and (most importantly) the sacred work they were participating in because without an accurate medical record the mission nurse and area medical advisor have to scramble to figure out the information the missionary hid from them in the first place.

Don't be discouraged by either condition - but please let your bishop know so that you and he can make a plan for your health care when you're away from home.