How long have you been doing...?
How long have you been learning English?
How long have you been reading the book?
be good at sth/doing sth
I'm good at speaking English.
A: How long have you been watching T.V.?
B: About 10 hours.
A: You need to get a job!
B: Why? You and dad make so much money.
A: You can't just sit around all day.
B: But I'm not good at anything.
A: Everyone is good at something.
B: Well, I'm good at watching T.V.
A: Why don't you become a T.V. critic?
B: I would love to watch T.V. and write great reviews!
A: See? You are good at something.
B: Thanks, Mom. I'll start looking for jobs now.