A great place to try your knife kills is in 'Squad Deathmatch' All the maps are small, its 4v4v4v4 so you'll have less chance of someone stealing your kill and your bound to run into the enemy.
I also feel that the Recon class would be the best class to do this with because the recon class has a 'Recon Beacon' Basically like a tactical insertion in Call of Duty, just place one down ina discreet location near the action. Equip the knife and you'll be sure to run into someone.
I wouldn't say this is easy as most Battlefield players by now are over Rank 100.
I got over 1000 Kills with the Machete and Iv done most of them in Squad Deathmatch, the others game modes are too big!
Team Deathmatch is also good but Iv noticed even when your in a squad it will spawn you by your kill stealing team mates and they will most probably give away your location.
In the clip I was using the Recon Class with the Recon Beacon and they didn't even notice me because there eyes were on my team mates while my Reccon Beacon gave me the upper hand to sneek up behind them, if I failed too I can spawn back on it and try again.
Two very good maps to get are 'Flood zone' and 'Hainan Resort'
On flood zone and Resort, most players go for the roof and if they don't catch you climbing up you can easily net yourself a few knife kills!