what are the 11 developmental tasks for adolescents?

I am not sure about all eleven, nut I believe that some include:

1. Seeking freedom from parental figures
2. Establishment of personal identity
3. Handling of sexual energies
4. Remodeling of former idealizations of self and others

Do you have any more information as to what exactly you are looking for?

Not sure where you got 11. I only found Havighurst’s eight here:

1. Achieving new and more mature relations with others, both boys and girls, in their age group.
2. Achieving a masculine or feminine social role.
3. Accepting one’s physique.
4. Achieving emotional independence from parents and other adults.
5. Preparing for marriage and family life.
6. Preparing for an economic career.
7. Acquiring a set of values and an ethical system as a guide to behavior—developing an ideology.
8. Desiring and achieving socially responsible behavior.

Then there’s the Eight Stages of Social-Emotional Development for teenagers developed by psychiatrist Erik Erikson in 1956.

I used this Google search

Maybe you can start there.

1 Shaping an identity
2 Becoming autonomous
3 Constructing and living out a value system
4 Being capable of a loving commitment
5 Reflecting on religion
6 Making friends and living with intimacy
7 Integrating sexuality
8 Gaining competence
9 Selecting a career and taking an adult job
10 Using leisure time for renewal
11 Taking part in the broader community

I think those are the ones you’re talking about.