How can I contact to

If you mean this one: Robert G. Schaffrath - Professional Profile[^] you can either find one of his messages: Latest Messages[^] and reply to it, or use the "Email" widget under the message body to send him a message.
Or, you can use his "@ name" to send him a message by entering it into a message - it's at the top right of his profile page - just as yours will send you one: @User-13742664

However, he doesn't appear to have logged in since 2014, so don't be too surprised if he doesn't reply, or if his email is not up to date.