Collector-Base capacitance in simple FM transmitter
In this circuit, collector-to-base capacitance would be close to \$C_{ob} \$. The base is almost grounded by C1 as far as radio frequency is concerned.
\$ C_{ob} \$ is typically 2.5pf, maximum of 4pf when the DC collector-to-base voltage is 5V.(From a National Semiconductor data sheet). This measurement was done at 1MHz, not at 100MHz where this circuit is usually meant to operate.
From the 2N3904 data sheet by ON semiconductor, \$C_{obo} \$ corresponds to collector-to-base capacitance:

This graph will not be useful if you wish to include \$ C_{ob} \$ in calculation of oscillation frequency, since \$C_{ob} \$ has a relatively minor affect on frequency, compared to other capacitances. Not shown on the schematic are stray capacitances and inductances, and the reactive component added by the antenna. Besides strays, the inductor's self-resonant frequency is likely unknown. Tolerance of small-value inductor and capacitors is often poor, and their values are modified by inductance of connecting wires.
At 100MHz, the 2N3904 hasn't much gain, and is likely running close to its gain*bandwidth limit: a carefully-done internal model would be required.
As others have said: you build it and verify that it oscillates by searching for its frequency with measurement tools. Then you vary component values in an attempt to move frequency up or down. (VC1 variable capacitor is meant to modify frequency, but 100pf seems somewhat too large). This is by no means a stable and predictable oscillator at 100 MHz.