If $x$, $y$, $k$ are positive reals such that \[3=k^2\left(\dfrac{x^2}{y^2}+\dfrac{y^2}{x^2}\right)+k\left(\dfrac{x}{y}+\dfrac{y}{x}\right),\] find the maximum possible value of $k$.
1. Given the equation:
   \[
   3 = k^2\left(\dfrac{x^2}{y^2} + \dfrac{y^2}{x^2}\right) + k\left(\dfrac{x}{y} + \dfrac{y}{x}\right)
   \]
   we need to find the maximum possible value of \( k \).

2. Note that for any positive real number \( a \), the inequality \( a + \frac{1}{a} \geq 2 \) holds. Applying this to our equation, let \( a = \frac{x}{y} \) and \( b = \frac{y}{x} \). Then:
   \[
   a + \frac{1}{a} \geq 2 \quad \text{and} \quad b + \frac{1}{b} \geq 2
   \]
   Since \( a = \frac{x}{y} \) and \( b = \frac{y}{x} \), we have:
   \[
   \dfrac{x}{y} + \dfrac{y}{x} \geq 2 \quad \text{and} \quad \dfrac{x^2}{y^2} + \dfrac{y^2}{x^2} \geq 2
   \]

3. Substituting these inequalities into the given equation:
   \[
   3 \geq k^2 \cdot 2 + k \cdot 2
   \]
   Simplifying, we get:
   \[
   3 \geq 2k^2 + 2k
   \]
   or equivalently:
   \[
   2k^2 + 2k - 3 \leq 0
   \]

4. To find the maximum value of \( k \), we solve the quadratic inequality \( 2k^2 + 2k - 3 \leq 0 \). First, we find the roots of the quadratic equation \( 2k^2 + 2k - 3 = 0 \) using the quadratic formula:
   \[
   k = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
   \]
   where \( a = 2 \), \( b = 2 \), and \( c = -3 \). Substituting these values, we get:
   \[
   k = \frac{-2 \pm \sqrt{2^2 - 4 \cdot 2 \cdot (-3)}}{2 \cdot 2}
   \]
   \[
   k = \frac{-2 \pm \sqrt{4 + 24}}{4}
   \]
   \[
   k = \frac{-2 \pm \sqrt{28}}{4}
   \]
   \[
   k = \frac{-2 \pm 2\sqrt{7}}{4}
   \]
   \[
   k = \frac{-1 \pm \sqrt{7}}{2}
   \]

5. The roots are:
   \[
   k = \frac{-1 + \sqrt{7}}{2} \quad \text{and} \quad k = \frac{-1 - \sqrt{7}}{2}
   \]
   Since \( k \) must be positive, we take the positive root:
   \[
   k = \frac{\sqrt{7} - 1}{2}
   \]

6. To verify, we check the inequality \( 2k^2 + 2k - 3 \leq 0 \) at \( k = \frac{\sqrt{7} - 1}{2} \):
   \[
   2\left(\frac{\sqrt{7} - 1}{2}\right)^2 + 2\left(\frac{\sqrt{7} - 1}{2}\right) - 3
   \]
   \[
   = 2\left(\frac{7 - 2\sqrt{7} + 1}{4}\right) + \sqrt{7} - 1 - 3
   \]
   \[
   = \frac{8 - 2\sqrt{7}}{2} + \sqrt{7} - 4
   \]
   \[
   = 4 - \sqrt{7} + \sqrt{7} - 4
   \]
   \[
   = 0
   \]
   Thus, the inequality holds, confirming that \( k = \frac{\sqrt{7} - 1}{2} \) is the maximum value.

The final answer is \(\boxed{\frac{\sqrt{7} - 1}{2}}\)