Davies' place-kicking was below par in Wales' 24-6 win over Tonga on Friday, missing three of seven chances, but the fly-half impressed with ball in hand.
Wales now travel from Eden Park to Apia to face Samoa on Friday, 23 June.
"Sam is the main danger for Wales. He's good at making the right decision at the right time, he's classy and he's got a good kicking game," Fonotia said.
"He is a very gifted player. He always seems to have a bit of time when he takes the ball to the line."
Fonotia joined Ospreys from New Zealand side Crusaders in February 2016 and his performances for the Welsh region have helped smooth his way into international rugby.
The 29-year-old, who was born in Christchurch but qualifies for Samoa through his grandfather, made his Test debut in the 78-0 thumping by New Zealand on Friday.
That match was part of a double-header at Eden Park, in which Wales saw off Tonga earlier in the day.
Fonotia will now make his first visit to his adopted country this weekend, hoping to put one over his Ospreys colleagues.
"I've never been to Samoa and it will be my first time, but I'm pumped to get there," Fonotia said.
"I caught up with a few of the Wales guys in New Zealand. I know they're looking forward to the game and playing against your mates is always fun.
"We want to give it a really good crack."
Samoa centre Kieron Fonotia has warned his international team-mates to watch out for Ospreys colleague Sam Davies.