Is the word onze the same in Brazilian and European Portuguese?

Yes

The spelling, meaning, and grammatical usage of "onze" are identical in both Brazilian and Continental Portuguese. The only difference is in pronunciation. In Brazilian Portuguese, the unstressed final "e" is typically pronounced as a high, closed vowel [i], making the word sound like "on-zee." In Continental Portuguese, the final "e" is a closed, unreleased vowel [ɨ], which sounds much more clipped, almost like a very short, neutralized "uh" sound.

Brazilian Portuguese Examples

1. Eu tenho onze reais na carteira. (I have eleven reais in my wallet.)
2. São onze horas da manhã. (It is eleven in the morning.)
3. Ele tem onze anos de idade. (He is eleven years old.)
4. Comprei onze laranjas na feira. (I bought eleven oranges at the market.)
5. O número onze é o meu favorito. (The number eleven is my favorite.)

Portuguese (Portugal) Examples

1. Eu tenho onze euros na carteira. (I have eleven euros in my wallet.)
2. São onze horas. (It is eleven o'clock.)
3. Ele tem onze anos. (He is eleven years old.)
4. Comprei onze laranjas no mercado. (I bought eleven oranges at the market.)
5. O número onze é o meu preferido. (The number eleven is my favorite.)