Praise when he licks will help. Praise is just positive reinforcement and works the same way as other kinds of positive reinforcement.
There's a lot of reasons a dog may not be licking besides not wanting to. He may have been trained not to before you got him or implicitly by you (dogs get trained in countless ways by you based on everything you do), he might have not come up with the idea to lick there yet, he might not know it is okay or encouraged, he might be too distracted by other things in the environment or habituated to doing other behaviors at that time that are incompatible (during sexy times, reading your excitement and wanting to play!), he might not have enough energy at that time or have too much energy. There are different tastes and smells after licking gets underway that he might like. For example, I know that when it comes to being kissed by one of my dogs he gets more excited the longer it goes on because my mouth becomes iron-y from he roughness of his tongue. Dogs also get rewarded internally by expending their energy if he decides to really get into it and he may enjoy the feel of licking like anyone orally focused, but these are things he would only be able to consider if he actually tries it.
There's reasons that can prevent licking before it starts and also rewards for licking that a dog can't consider before trying it because dogs don't plan ahead. There's different motivations a dog might have for licking that have different factors that encourage/discourage it.
The only way to know how a dog feels about it is to experiment and see how he responds to different circumstances. You won't know for sure until he's actually doing it. Positive reinforcement can help him actually try it, then see how he feels and if he is motivated to continue without it. Listen to his wishes.
