I wonder if I do this all the variables will be public or just the first one:
public string equipamento, marca, modelo, descricao, observacoes, prioridade;
Or if I need to declare them like this:
public string equipamento;
public string marca;
public string modelo;
[...]
The second option obviously works, but does the first one too?
As explained in the C# language specification, section 10.4 Fields on MSDN:
A field declaration that declares multiple fields is equivalent to multiple declarations of single fields with the same attributes, modifiers, and type. For example
class A { public static int X = 1, Y, Z = 100; }
is equivalent to
class A { public static int X = 1; public static int Y; public static int Z = 100; }
But as commented by @hyde, consider the former bad practice. It actively harms the readability of your code.