$f, g\in C^1(I) $ where $I$ is an open interval and $f, g$ both are real valued.
Let $W(f,g)(x) =\begin{vmatrix}f(x) &g(x) \\f'(x)&g'(x)\end{vmatrix}$ denote the Wronskian of $f, g$ at $x\in I$
$\textbf{Question}$ Does there exists such $f, g$ for which $W(f, g) (x) >0$ for some $x$ and $W(f, g) (x) <0$ for some $x$ ?
$W(f, g) (x) \neq 0$ for some $x\in I$ implies $\{f, g\}$ linearly independent.
If two functions are solutions of a differential equation $y"+p(x) y'+q(x) y=0$ on $I$ where $p, q\in C(I) $ then by Abel's identity we have
$$W(f, g) (x) =W(f, g) (x_o) e^{-\int_{x_0}^{x} p(t) dt}$$
Then $W(f, g) (x_0) \neq 0$ for some $x_0\in I$ implies $W(f, g) \neq 0$ on $I$
Moreover $W(f,g)$ different from zero with the same sign at every point ${\displaystyle x} \in {\displaystyle I}$
Hence we have to find two functions $f, g$ with the properties:
$f, g$ must have to be linearly independent.
$f, g\in C^1(I) $
$f, g$ can't be the solution of $2$nd order homogenous linear ODE.
$W(f, g) $ attains both positive and negative values on $I$.
Let $0\in I$ be an open interval and $f, g\in C^1(I) $ defined by $f(x) =x^2$ and $g(x) =x|x| $
Then $f,g$ satisfy $1, 2,3 $ but not $4$ as $W(f, g) (x) =0$ on $I$.