Given the problem, we start by understanding the properties of an ellipse. The sum of the distances from any point on the ellipse to the foci is constant and equal to $2a$, where $2a$ is the length of the major axis.

1. From the given condition $|PF_{1}|+|PF_{2}|=2\sqrt{6}$, we understand that this sum equals the length of the major axis, hence $2a=2\sqrt{6}$. This directly leads to finding the value of $a$:
$$2a = 2\sqrt{6} \implies a = \sqrt{6}.$$

2. Knowing that the point $P(2,1)$ lies on the ellipse, we can substitute its coordinates into the ellipse equation:
$$\frac{{2}^{2}}{{a}^{2}}+\frac{{1}^{2}}{{b}^{2}}=1 \implies \frac{4}{6}+\frac{1}{{b}^{2}}=1.$$
Solving this equation for $b^2$ gives us:
$$b^{2} = 3.$$

3. The distance between the foci of an ellipse, $|F_{1}F_{2}|$, is given by $2c$, where $c$ is the linear eccentricity of the ellipse. The relationship between $a$, $b$, and $c$ is given by $c^{2}=a^{2}-b^{2}$. Substituting the values of $a$ and $b$ we found:
$$c^{2} = a^{2} - b^{2} = 6 - 3 = 3.$$
Therefore, $c = \sqrt{3}$.

4. Finally, the distance between the foci $|F_{1}F_{2}|$ is $2c$, which gives us:
$$|F_{1}F_{2}| = 2\sqrt{3}.$$

Therefore, the answer is $\boxed{2\sqrt{3}}$.