Ksana deals entirely skill damage, so any support that buffs skill damage will be good for her.
Siris also deals Thermal damage, so Thermal-damage buffs are also useful to her.
Unlike most main dps operatives though, Siris' damage is largely based on her Max HP, and only partially based on her ATK.
ATK buffs are thus less useful for Siris than for other dps operatives.
This makes support operatives who can only buff ATK (e.g. Eatchel - The Cub) much less useful for Ksana than for other dps operatives.
Ksana has very high HP and naturally gains some damage reduction effects, and thus Ksana can have very good survivability, although somewhat reduced due to her proximity to enemies.
This means Ksana does not necessarily need healing as much as other operatives.
Support operative that work well with Siris - Ksana:
Vidya - Celestial Swan (and other resistance shredders)
Celestial Swan and other resistance shredders (Acacia - Kaguya, etc.) that reduce the enemies resistance help enemies take more damage.
If using Celestial Swan, make sure the other support isn't off element to Ksana.
Siris - Freefin
Ksana deals skill damage very rapidly, allowing her to easily gain Siris' Wavehunt, and trivially maintain Freetide, and Siris provides lots of skill damage buffs to Ksana.
Freefin's +ATK boosts are less useful for Ksana though, but she's still a great support for Ksana.
Marian - Riptide
Riptide provides some nice skill damage buffs to Ksana.
Note that Riptide is off-element to Ksana (Riptide deals Chaos damage)
A lot of the usual cope Supports like Agave and [Redacted] etc. don't work well with Ksana as Ksana gains less benefit from ATK buffs than other operatives.
Chenxing - The Observer's skill buffs are useful, but Siris' mobility and ability to push enemies can make it difficult to stay in Chenxing's AoE. This makes Chenxing difficult to use with Ksana.
Tess - The Magician is generally wasted on Ksana, as Ksana's ult requires only 15 U-Energy, and mostly wants Resilience stacks, which Tess doesn't help with.
As such Tess doesn't really help Ksana that much.
Tess' damage buffs are still useful, but overall Tess isn't a great support as her damage buffs are weak in comparison to actual skill damage supports like Freefin.
Since Ksana never actually shoots anything, she'll never charge the Zephyr Machine from Enya - Exuvia's support skill, and hence it will never deal damage.
Enya's skill damage buffs are still ok, but overall Exuvia isn't a great support for Ksana.
Not shooting anything means that per-shot aptitude buffs like Tess - Phantasia and Fritia - Little Sunshine are wasted on Ksana.