Okay, I've been thinking about this one because apparently no one ever did this before.
This is what each demigod (the one I could have think to) smells like, but in real terms:
Percy Jackson: smells like sea. "Cloud Collection n.3" by Zarkoperfume.
Annabeth Chase: smells like books, elegance. "Joy" by Jean Patou.
Thalia Grace: smells like forest and rain. "Devil's Nightcap" by Lush.
Jason Grace: smells like rain's air. "The smell of weather turning" by Lush.
Piper McLean: smells like fruits, beauty. "Imperatrice" by Dolce & Gabbana.
Nico di Angelo: smells like earth. "Baccarat Rouge 540" by MFK.
Will Solace: smells like summer in the USA. "Opium" by Yves Saint Laurent.
Clarisse La Rue: smells like impulsivity, danger. "Marijane" by Alyssa Ashley.
Frank Zhang: smells like sense of power. "Creed"
Hazel Levesque: smells like cold but warmth at the same time. "Pure musc" by Narciso (white edition).
Leo Valdez: smells like fire and mechanism. "Fahrenheit" by Dior.
Silena Beauregard: smells like love and femininity. "Narciso for her" by Narciso Rodriguez.
Drew Tanaka: smells like vanity who stuns you. "Bright Crystal" by Versace.
Grover Underwood: smells like nature. "Neroli Portofino" by Tom Ford.
Coach Gleeson Hedge: smells like masculinity and strength. "Black Musk" by Montale.
Mellie the nymph: smells like grace. "Chloé" by Chloé.
Reyna Avila Ramírez-Arellano: smells like something who can overwhelm you. "Ayurveda" by Tesori d'oriente.
Hylla Ramírez-Arellano: smells like wealth. "J'adore -dior-" by Dior.