How to echo Widget Title in Custom Frontend-Template Box

You should not use echo in this case. Please visit the function reference of get_template_part. As you will see, there is nothing to print:

get_template_part doesn’t return a value and doesn’t warn if it fails
to find a matching template file.

Additionally, I recommend that you check out this question: Should we use get_template_part() in functions files instead of include_once?