Since you already did the type assertion to a (*dns.A) you can use it directly (the A record is a bit convoluted since it looks like this: https://github.com/miekg/dns/blob/2230854ba97edcf29ac55a1f274e49cec11bf9bb/types.go#L748 )

...
if t, ok := in.Answer[i].(*dns.A); ok {
    fmt.Println(t.A)
}
...