There is some device to measure the string tension. it cost around $100 to $150 dollar. But first of all , you need to understand string tension is changing all the time. so even you got your testing device. you make the measurement after restring, after 1 day. you recheck it again. The measured figure will not be the same. This is common for all the string. So I can say your testing results will always show "吾足磅" .
First of all, if you are a rookie (as you said you are), there's almost no point in knowing if your string tension is correct. As someone who hasn't had enough experience to tell if the string is at his specified tension, you should try playing with your current tension first. If you feel that you get too little power, like you're playing with a frying pan made of stone, and you want more "ball pocketing" before the ball leaves your racket, then you definitely should lower your tension a little bit next time your string. If on the other hand, you feel like the ball "explodes" to a spot on the court much longer than you expect to play to, and find it kind of uncontrollable, then you should consider increasing your string tension (and definitely not shorten your swing, or put less power to your shot, but try putting more top spin if possible) a bit next time.
While there are indeed some devices (I find only one on the internet though) that checks the tension AFTER a racket is strung, I don't think they are as cheap as the other member in this forum mentioned. Those that cost at around the $100-150 mark are for calibrating stringing machine, BEFORE the racket is strung. Those that check tensions on a strung racket could cost as much as $500. And for that kind of money you can have 2 to 3 more string jobs, or even more if you have access to a machine. Plus who knows how accurate those devices are? How much of a difference is 1 lbs? Not much, but it plays differently on a tennis racket(for some people).
The only way, in my opinion, to check if your current string job is in fact of the correct tension, is to string the exact same racket again, with the exact same string, at the exact same specified tension, preferably by a different person in a different shop. If it feels drastically different from the last time... even that does not tell you anything, because it only tells you that the two string jobs are different. There's still no way to tell which one is right, and which one is wrong; or they could both be wrong!
So, my advice is: just get on with it. Play more tennis, get "acquainted" with your (new) racket and strings (preferably a variety of strings). And by getting more experience you'll know what kind of strings and tension you want that's best for you.