That kind of exponential function doesn't have any vertical asymptotes. "That kind," meaning of the form you provided:
[tex]f(x)=ab^{x-h}+k[/tex]
Having a vertical asymptote (basically) means there is a non-removable discontinuity for some value of x. The given f(x) will be defined for all values of x, so it's continuous and thus has no vertical asymptotes.
