Who is killed in the assasination attempt on senator Amidala?

It seems likely that after ten years and after becoming senator she chose another double after Sabé (and with the Nabooans' heavy make-up the double doesn't necessarily need to look much like Padmé anyway ;-)).

While the English Wikipedia article doesn't give much information on this, its German version says that it was a double named Cordé, which IMDb seems to agree with:

Cordé was a handmaiden and double for Senator Padmé Amidala of Naboo.

Cordé replaced Amidala's former decoy, Sabé, who was a decoy while Amidala was Queen of Naboo.

She was killed in an assassination attempt on Amidala when she returned to Coruscant for the Senate vote on the Military Creation Act. The person responsible for the attack was bounty hunter Zam Wesell, who worked for the Confederacy of Independent Systems via fellow bounty hunter Jango Fett.

Cordé died apologizing to Amidala, disheartened in thinking she had failed her duty to the Senator. On the contrary - Padmé was heartbroken by Cordé's sacrifice, regrettably accepting that she had perfomed her duty in order for the Senator to proceed with her vote for the Military Creation Act. Reluctantly, she left the bodies of Cordé and the other Royal Guards behind, guilt stricken over their rising to the greater good at the cost of their lives.

In addition to that, she is also directly mentioned in the script and the movie made out of this script:

Klaxons blare, alarms sound! CAPTAIN TYPHO and the TWO ESCORT PILOTS get up and run to where SENATOR AMIDALA lies dying. Beyond, ARTOO DETOO drops down from the Naboo Fighter and rolls toward the wreckage. The FEMALE ESCORT PILOT kneels by SENATOR AMIDALA and takes off her helmet, revealing SENATOR PADME AMIDALA.

PADMÉ: Cordé...

She gathers up her decoy double in her arms. Cordé's eyes are open. She looks up at her.

CORDÉ: ... I'm sorry, m'lady... I'm... not sure I...

CORDÉ dies. PADMÉ hugs her.

AMIDALA: No!... No!... No!...

PADMÉ lowers CORDÉ to the ground. She gets up and looks around at the devastation. There are tears in her eyes.

AMIDALA: I should not have come back.

CAPTAIN TYPHO: M'Lady, you are still in danger.

Amidala says nothing.

CAPTAIN TYPHO: This vote is very important. You did your duty and Cordé did hers. Now come. (she doesn't respond) M'Lady, please!

According to novelization of Episode II by R.A. Salvatore, it was her bodyguard Cordé

"Cordé," she said quietly, her voice breaking. Cordé was one of her beloved bodyguards, a woman who had been with her, serving her and serving Naboo, for many years. Padmé gathered Cord up in her arms, hugging her gently.

...

Captain Typho came up out of his ready stance long enough to lock stares with his Senator. "This vote is very important," he reminded her, his tone uncompromising, the voice of a man sworn to duty above all else. So much like his uncle. "You did your duty, Senator, and Cordé did hers. Now come." He started away, grabbing Padmé's arm, but she shrugged off his grasp and stood there, staring down at her lost friend. "Senator Amidala! Please!" Padmé looked over at the man. "Would you so diminish Cordé's death as to stand here and risk your own life?" Typho bluntly stated. "What good will her sacrifice be if--"