Say we have a $n \times m$ matrix $\boldsymbol{X}$. When we see $\boldsymbol{X}^T_i$, is this typically referring to
(1) the i-th row of $\boldsymbol{X}^T$, which is a column vector. So $\boldsymbol{X}^T_i$ is $m \times 1$
(2) the i-th row of $\boldsymbol{X}$, which is a column vector, then take its transpose, giving us a row vector? So $\boldsymbol{X}^T_i$ is $1 \times n$.
I always get confused with notation in vector calculus. Is there a standard/popular usage?
I fully subscribe to davidlowryduda's comment. Thus, I would first specify that $X_i$ denotes the $i$-th column of $X$ and then, to avoid any ambiguity, I would write $(X^T)_i$ for (1) and $(X_i)^T$ for (2).