You can start by looking on Archive of Our Own (AO3). It has a vast collection of fanfictions, and there are many bruce x clark ones there. Just use the search function and type in 'bruce x clark' and you'll get a bunch of results.
I also recommend 'The Dawn of a New Alliance'. In this story, Bruce and Clark start to form a relationship not just as allies but also as friends who understand each other on a deeper level. It shows their different perspectives on justice and how they can complement each other.
The theme of secrecy and revelation is also quite common. They are superheroes, and a pregnancy in this situation can be a big secret to keep. So, fanfictions often play with how they hide it from others, and when and how they finally reveal it. It adds an element of suspense and drama to the story.
Another theme is the power dynamics. Given that both Clark and Bruce have their own unique powers and resources in the DC universe, fanfictions might play with how these powers interact in the context of their relationship. It could be about one protecting the other or them working together in a new way.
There's also 'A New Beginning'. This fanfiction focuses on the emotional journey of Clark and Bruce as they prepare for the arrival of their child. It's full of heartwarming moments and interesting character development.
The theme of secrecy and trust also pops up a lot. Clark has his secret identity as Superman, and Bruce is Batman. They have to learn to trust each other with their true selves. Fanfictions often explore how they come to terms with this, like in the story where Bruce discovers Clark's identity and has to decide whether to keep his trust or expose him. This creates a lot of tension and drama in the stories.
One great 'Bruce Wayne x Clark Kent' fanfic is 'The City of Two'. It beautifully weaves their complex relationship, exploring how their different identities interact in a romantic context. The characterizations are really on point, staying true to the essence of both Bruce and Clark from the original comics while adding a new layer of intimacy.
Some specialized superhero or DC Comics fan communities may also host or recommend Clark x Bruce yaoi fanfiction. These communities often have members who are really into specific pairings and can point you in the right direction. For example, on Reddit, there might be relevant subreddits where fans share and discuss such fanfictions.
The theme of trust is very prominent. Given their different backgrounds and methods, it takes time for them to fully trust each other in fanfics. And then there's the theme of love - whether it's platonic or romantic. Their relationship is often a central focus, with how they support and care for each other in different situations, be it in a fight against a powerful villain or just in their daily lives.
One common theme is the contrast between their personalities. Clark is often seen as the more open and friendly one, while Bruce is the brooding and mysterious type. Their relationship in these fanfictions usually explores how they balance each other out.