Unless you are a Jedi Guardian this is probably the most difficult achievement in the game alongside the Mandalorian battle circle one. Once you get to the end of Telos you will have the opportunity to speak with the handmaidens. Tell one that you are looking for a fight and she will accept sending you to a sparring mat. You have to complete progressively more difficult fights but you also get access to more of your abilities and items as well.
For the first fight you will only be able to use unarmed combat: no weapons, items, or force powers. If you are a Jedi Guardian this shouldn't be a problem, you can just skip ahead to the next part. Sentinels and Consulars with high Strength, Dexterity and Constitution might also be okay but since those are otherwise largely useless skills (except maybe Dexterity) for those classes you hopefully haven't invested too much in them. Instead you pretty much have to rely on luck to win here. You can pause and save at any time so just save after every good hit and load after you get pounded. I recommend just using normal attacks here since power attack just lowers your already poor chances to hit and and flurry and critical strike will leave you even more open to being hit. Since leaving the mat counts as a forfeit you can also try kiting her around the edge in the hope that she accidentally steps out.
The second fight is the same as the first except you are allowed to use melee weapons. This will make it even easier for a Guardian and about the same for the others. Sentinels and Consulars should just repeat the strategy from the first fight.
The third fight allows use of all weapons, items and force powers. Here is where Consulars can finally shine. Just blast her with force lightning or stasis and you win. For sentinels, if you have a melee shield equip it immediately and then load up on stims before using your preferred weapon and force powers.
The fourth fight is the same as the third but with two handmaidens instead of one. Repeat your strategy from before but you will probably need to use medpacs. Also, if you back yourself into a corner and spam force whirlwind on one of the handmaidens the other one needs to pass a save or be thrown to the side, usually off the mat.
The fifth fight is definitely the most difficult. You fight all five of the handmaidens at once with two in front and three behind. The whirlwind trick is really a must here, maybe even for Guardians unless they're pretty optimized. Get into a corner and spam it until you only have one or two handmaidens left and then defeat them normally. Alternatively, if you can line them up right force lightning can be extremely devastating as well. Finish them off and the achievement will pop.