  We study the spectral dimensions and spectral asymptotics of Krein--Feller
operators for weak Gibbs measures on self-conformal fractals with or without
overlaps. We show that, restricted to the unit interval, the $L^{q}$-spectrum
for every weak Gibbs measure $\rho$ with respect to a $\mathcal{C}^{1}$-IFS
exists as a limit. Building on recent results of the authors, we can deduce
that the spectral dimension with respect to a weak Gibbs measure exists and
equals the fixed point of its $L^{q}$-spectrum. For an IFS satisfying the open
set condition, it turns out that the spectral dimension equals the unique zero
of the associated pressure function. Moreover, for a Gibbs measure with respect
to a $\mathcal{C}^{1+\gamma}$-IFS under the open set condition, we are able to
determine the asymptotics of the eigenvalue counting function.
